I have no idea. I hate Gravatar. It's slow and refuses to ever finalize anything. You can even change your username if you mess with your account settings. -_-
Gravatar is not linked to any username at all, it is for emails. I'm pretty sure you can even add new emails onto the same account. Gravatar doesn't have any issues at all, you must be using it wrong.
For a gravatar to show up, you need to have registered with the SAME email on this (or other) site that you used with gravatar. (After that, it may take about 10 minutes to show up on other sites)