Gravatar often fails to load on Import Repository page

Tiny issue, but in using the Bitbucket importer for about 100 repositories, I've noticed that my account Gravatars only successfully load approximately half the time. The rest of the time, they are shown as blank white squares.

See attached screenshot for example.

Behavior observed in Chrome and Chromium on Mac OS X and Linux, have not yet attempted to look in other browsers or on Windows.