It seems the Gravatar support is not working well in JIRA 6.4. See https://confluence.atlassian.com/display/JIRA/Adding+a+User+Avatar?focusedCommentId=728139293#comment-728139293:

Just installed 6.4.1 which is supposed to support gravatars at the same time as custom and built-in avatars. It kinda does, but so far it is behaving weirdly. The documentation on this page says your gravatar should appear as one of the choices the dialogue; it does but it appears many times in all the spots where you had custom images. It still displays the custom image, not the gravatar. On the other hand, if you choose a built-in avatar the your gravatar is displayed.
So the actual functionality appears to be if you have gravatars enabled and you have a gravatar, that appears to override any built-in avatar but not custom images. When a gravatar override is in effect, you'll see a 'GRAVATAR' icon underneath your image in the profile editor.
That functionality is ok, except that the person implementing that apparently wasn't following the same blueprint as the people implementing the avartar editing dialog and documentation (smile)
It this how it is working for other 6.4.1 users?