Every time I click the "Ask Question" button on Area 51 Meta, it changes any profile picture I have to a default gravatar. Further clicks of the "Ask Question" button just generate a different default gravatar.
Note that it only changes the profile picture for Area 51 meta and leaves pictures as-is on all other sites.
Gif added - Ask Question each time opened in new tab, then closed. Rinse & repeat 4 or 5 times.