Accepting a group invitation does not update the page
When accepting a group invitation, the "Join Group" button / link does cause the current user to be added to a group, but doesn't update the page to reflect any new state (removing the button / link and updating the group membership lists).
Ping @manthey .
I confirm that this is still an issue on data.kitware.com, after inviting user to be administrator of a group. There are still listed as "Pending" despite the fact there are effectively listed as Administrators.
Note also that they are not listed as members of the group either.
+1 Observation of this bug. :-)
Just ran into this myself.