Comment 7 for bug 946956

In my case, the problem was fixed after I logged out then logged in as root to delete all the hidden folders+files in my user's home folder (except for several specific folders+files). I do this cleanup every few years, and it always seems to fix a few bugs (my home folder has its own partition so it survived my clean install of Ubuntu 12.04). I don't suggest that this is a reasonable solution, but it should narrow down what the problem is.