Contacts showing up as "Removed" from Group when they're actually a current member

This is an issue I'm not able to recreate.

In the display of all the group members in a group, one contact shows up as "Removed". When I view his contact record, it says he's a (current) member of the group. Other group-related functions work as if he IS a member of the group (i.e. when sending an email to the group, his name shows up in recipient list). It's as if the display is not refreshing.

This happened with another contact in the same group. I removed him, signed out of CiviCRM, signed back in and added him. Nothing seemed to change but when I signed back out again, his group membership was corrected (he was displaying as a current member both in the group list and from his contact record).

I don't know how this happened so I can't reproduce it but I have screen shots if they would be helpful.