The changes window is missing revisions in the svn repository. In the attached image, one of the files show a revision that does not show up in the list of revisions in the repository (the one from 10:41).
The incoming changes tab is also behaving erratically. There have been lots of times lately when it should have contained incoming changes (and subsequent updates confirmed my expectations, there were changes, just not visible in there).
Clearing the vcs caches didn't help.
The eclipse projects inside the workspace are checked out from various locations in the repository (the directory structure is quite elaborate), not sure if this matters as well.
After cleaning up the entries and manually adding the good ones, the problem went away.
I wouldn't say the problem is invalid, though, since it's quite a confusing situation and IDEA should handle it in a better way (or at least signal the vcs config issues somehow).