There is a time delay before the new gravatar populates throughout the internet. You may also want to check very carefully what is said on the gravatar site in the FAQs as it contains common questions and answers to them http://en.gravatar.com/site/faq/
These are the best practices for uploading your gravatar:
(1) Prepare the image prior to uploading it and make sure it’s 512 x 512 pixels or larger so it will look the best in the widest range of uses.
(2) The image filetype has to be either PNG, GIF or JPG. Make sure the file name contains only letters and numbers – no special characters – and make sure all letters are in lowercase.
(3) Also make sure the image file name has an extension (Example – image.jpg)
P.S. The first place we tend to see that change take place is here in the forum.
I hope this helps. Best wishes with your blogging. :)