On some fatal errors you lose the channel settings and window settings. The information that you have read the basic information about GRs, gogus and cupboards seems to be lost to (at least I got informed how they work in my primary appartment). And you receive a mail from your skill advisor.
The latter isn't that much of a problem, but the other ones are pretty annoying.
I haven't had one of those fatals on the testserver yet (don't know how to provoke those) but I assume the behaviour is still there (maybe someone can confirm this).