I've been experimenting a bit with themes in Mint 13, both from the repositories and gnomelook.org.
Now when I log in I'm reverted to some strange theme and icon set.
When I change window borders in that particular theme and icon set, everything is ok until next login. There is a exclamation mark bellow the active theme and a message about matefaenzadark not properly set... or something. And I do indeed have faenza icons installed, including matefaenzadark subset.
At the same theme another user when logged in is having no problems with the same theme/icon set configuration.
I suppose it's some kind of permittions problem, I even deleted most of the previously installed themes, but manually I couldn't find anywhere matefaenzadark file, nor in "/home/.local/.themes/" nor in "/usr/themes/" directories...