Two different default gravatar images for the same user

All of our GitLab users who have not set their profile Icon have two different icons: the one shown at the top of the profile page, and a different icon for any/all activity. This is very visible/slightly confusing on each user’s profile page.

I’ve attached a screenshot of the issue.

I’m running GitLab CE 8.11.5. Gravatar is enabled. This issue only seems to exist for LDAP users. Users who have set their profile image (or their Gravatar) do not have this issue.

Any suggestions?