If you or anyone else does see the problem happen again, providing the post link, the expected YouTube video link, the actual YouTube video link, and a screenshot would be helpful especially if you need to update the post right away which is understandable.

Has the issue been resolved?

Thanks again.

Here's an example post:

http://janolofbengtsson.com/2012/06/15/anne-marie-david-je-suis-lenfant-soleil/

The one you suggest is not an example.

I can see no trace of the problem in the post revisions of any example post. All that I have this far been able to see there is the original postings, and then the updates through which I restored the original videos.

The latter were first replaced by this one, when it was my latest YouTube favourite:

http://www.youtube.com/watch?v=aaJ9KaY_TY8

In turn, that video was replaced by this one, when I added it to the favourites:

http://www.youtube.com/watch?v=wdhrAGXl3_0

Thanks.

I realize I should have left a post where the problem could be seen in action. It is now too late for that, since I felt I had to restore immediately.

Restoring them totally makes sense. It does still help to have a link to an example post though. One thing we could do is try looking at the post revisions. I did look through your blog and found this as a possible example: https://janolofbengtsson.wordpress.com/wp-admin/revision.php?revision=18777&action=edit

The post revisions look normal to me though, so it was a good thing to check but appears we need more info.

I will have to come back to you if this happens again: I will then immediately post here 1, 2 & 3. Thanks again.

Yes, please post more details if you find anything. There's not enough info to go on in this thread by itself and without an example.

I see that three others have had the same problem. Perhaps it can be solved with their help?

Yes, need more details!

Is there anything else that can help?

Disable post by email > http://en.support.wordpress.com/post-by-email/
Go to your email program and change the password now to a very difficult one

Change your blog password to a very difficult one > http://en.support.wordpress.com/passwords/#change-your-password

You have two separate email address settings at WordPress.com.
Blog notifications for the admin (like comment moderation, Likes, new subscriptions, etc) are sent to the email address at Settings -> General in the Dashboard.
Personal notifications (like comments on your post, subscription emails, and upgrade renewals) are sent to the email address at Users -> Personal Settings in the Dashboard.
http://en.support.wordpress.com/email-address/
http://en.support.wordpress.com/email-notifications/

The problem site is http://mrsmonizdotcom.wordpress.com/. I have a few blogs on my account, but this one is one that I did not create.
Blog url: http://mrsmonizdotcom.wordpress.com/

It is very likely that you were using the same password on WordPress.com that you used elsewhere. Recently, a few large services -- LinkedIn, Yahoo, eHarmony, and Last.fm to name a few -- have suffered well-publicized security breaches that have exposed email addresses and passwords. Although the passwords are usually stored securely, simple passwords can be decrypted or "cracked" in a matter of hours using modern technology.

Hackers gather the lists of email addresses and passwords from these services and then try to use them to access accounts on other popular services, like WordPress.com. If you used the same password multiple places, then your account can be compromised. That is what happened here. We do have measures in place to protect password guessing or "brute force" attacks but in this case, since the password is known beforehand, there is no need for a hacker to guess.

You should have a strong, unique password for every account you have on the internet. We have some more information on selecting a strong password in our Support section, please read through it:

http://en.support.wordpress.com/selecting-a-strong-password/

If you have any additional questions about the security of your account, please contact us using the form on this page:

http://automattic.com/security/

We take security seriously, and are happy to answer any questions you have.

It is very likely that you were using the same password on WordPress.com that you used elsewhere. Recently, a few large services -- LinkedIn, Yahoo, eHarmony, and Last.fm to name a few -- have suffered well-publicized security breaches that have exposed email addresses and passwords. Although the passwords are usually stored securely, simple passwords can be decrypted or "cracked" in a matter of hours using modern technology.

Hackers gather the lists of email addresses and passwords from these services and then try to use them to access accounts on other popular services, like WordPress.com. If you used the same password multiple places, then your account can be compromised. That is what happened here. We do have measures in place to protect password guessing or "brute force" attacks but in this case, since the password is known beforehand, there is no need for a hacker to guess.

You should have a strong, unique password for every account you have on the internet. We have some more information on selecting a strong password in our Support section, please read through it:

http://en.support.wordpress.com/selecting-a-strong-password/

If you have any additional questions about the security of your account, please contact us using the form on this page:

http://automattic.com/security/

We take security seriously, and are happy to answer any questions you have.

It is very likely that you were using the same password on WordPress.com that you used elsewhere. Recently, a few large services -- LinkedIn, Yahoo, eHarmony, and Last.fm to name a few -- have suffered well-publicized security breaches that have exposed email addresses and passwords. Although the passwords are usually stored securely, simple passwords can be decrypted or "cracked" in a matter of hours using modern technology.

Hackers gather the lists of email addresses and passwords from these services and then try to use them to access accounts on other popular services, like WordPress.com. If you used the same password multiple places, then your account can be compromised. That is what happened here. We do have measures in place to protect password guessing or "brute force" attacks but in this case, since the password is known beforehand, there is no need for a hacker to guess.

You should have a strong, unique password for every account you have on the internet. We have some more information on selecting a strong password in our Support section, please read through it:

http://en.support.wordpress.com/selecting-a-strong-password/

If you have any additional questions about the security of your account, please contact us using the form on this page:

http://automattic.com/security/

We take security seriously, and are happy to answer any questions you have.

It is very likely that you were using the same password on WordPress.com that you used elsewhere. Recently, a few large services -- LinkedIn, Yahoo, eHarmony, and Last.fm to name a few -- have suffered well-publicized security breaches that have exposed email addresses and passwords. Although the passwords are usually stored securely, simple passwords can be decrypted or "cracked" in a matter of hours using modern technology.

Hackers gather the lists of email addresses and passwords from these services and then try to use them to access accounts on other popular services, like WordPress.com. If you used the same password multiple places, then your account can be compromised. That is what happened here. We do have measures in place to protect password guessing or "brute force" attacks but in this case, since the password is known beforehand, there is no need for a hacker to guess.

You should have a strong, unique password for every account you have on the internet. We have some more information on selecting a strong password in our Support section, please read through it:

http://en.support.wordpress.com/selecting-a-strong-password/

If you have any additional questions about the security of your account, please contact us using the form on this page:

http://automattic.com/security/

We take security seriously, and are happy to answer any questions you have.

It is very likely that you were using the same password on WordPress.com that you used elsewhere. Recently, a few large services -- LinkedIn, Yahoo, eHarmony, and Last.fm to name a few -- have suffered well-publicized security breaches that have exposed email addresses and passwords. Although the passwords are usually stored securely, simple passwords can be decrypted or "cracked" in a matter of hours using modern technology.

Hackers gather the lists of email addresses and passwords from these services and then try to use them to access accounts on other popular services, like WordPress.com. If you used the same password multiple places, then your account can be compromised. That is what happened here. We do have measures in place to protect password guessing or "brute force" attacks but in this case, since the password is known beforehand, there is no need for a hacker to guess.

You should have a strong, unique password for every account you have on the internet. We have some more information on selecting a strong password in our Support section, please read through it:

http://en.support.wordpress.com/selecting-a-strong-password/

If you have any additional questions about the security of your account, please contact us using the form on this page:

http://automattic.com/security/

We take security seriously, and are happy to answer any questions you have.

Corrigendum: For "with precisely the same", read "precisely the same".

Thanks for your reply. I realize I should have left a post where the problem could be seen in action. It is now too late for that, since I felt I had to restore immediately - it looked truly absurd, and I knew my readers would immediately see it - the posts' original videos or other YouTube uploads of the same thing (in many cases there are several to choose from, and in restoring, I first didn't check if I used precisely the same; in some cases, I can't even do that at all, since I don't remember which version I used the first time). I suppose I will have to come back to you if this happens again: I will then immediately post here 1, 2 & 3. Thanks again.

Yes, I saw that timethief had modlooked this. I was thinking I should learn about it in order to be able to do it myself if there is another problem in the future. You have now given further help with that - thanks again.

The reason the videos you see match the titles is that I restored the original videos. In some cases I used other YouTube uploads of the same thing, but in others - I have now checked this - with precisely the same as in my original posting. This means that the change of videos had nothing to do with their being removed from YouTube.

I also see that videos that have been removed from YouTube have not been replaced: the imageless black and the message still appear as usual.

http://en.support.wordpress.com/passwords/#choosing-and-using-good-passwords