So right in the middle of the session, after i've decided to replace multisample with a single sample my BB stopped showing the contents of the card, all except of two files which were in the root. I've rebooted few times, took the card and in out, and finally plugged it in my laptop, where i saw that all the folders are hidden now. I'm pretty sure it happened on the box because i could see them when i turned on the BB and they weren't hidden for some time, while i was working on a pattern...might be wrong of course.