It happened two times in the last month that the content directory of the current month was erased. In both cases everything else was still there, other months as well as e.g. all images, even those uploaded recently.
It happened again. I don't see any suspicious access in the logs, so i don't think it's an attack from the outside.
I got another report that the problem is with the "view_counter.txt" files. The relevant code of that is around line 90 in scripts/sb_comments.php. I should probably add an option to disable that block of code if it is causing problems.
I added a setting to disable the view counter in svn r258 as a workaround since this bug doesn't seem to effect everyone.