You're correct that all of your comments should appear in My Activity. It looks like a bug that sometimes a comment is left but isn't connected in our database to the correct user account. On our end it simply appears that you weren't logged in when you left the comment. That shouldn't be possible, so we're trying to figure out how it may have happened.
Any more details about the steps you followed on your end would certainly help. You mentioned using the iPad app. Was this for the comment left on jaschmehl.wordpress.com ? I guessed that you would have left this comment by following these steps:
1. In iPad app, click Reader
2. View the post on jaschmehl.wordpress.com
3. Enter your comment
4. Click Post Comment
If I've got this wrong, and you actually left your comment a different way, can you let me know?
I have a suggestion for you as well which may help -- I recommend completely signing out of the iPad app, revoking its access, and then re-authorizing it by signing in again. The exact steps are these:
1. In the iPad app, click Settings
2. Click "Sign Out"
3. Make sure your iPad app is up to date (no little red number appearing in the corner of the icon)
4. From a browser, visit the My Apps page in your account settings
5. Click the "Remove Access" button for WordPress for iOS
6. On the iPad, launch the WordPress app
7. Sign into your account
In case there was some kind of glitch with your login status on the app, the steps above should reset everything to ensure that you are properly logged in.