That *could* be based upon your microSD card. How big is it? How full is it? How often do you swap files on and off the card (defrag it)? Whats the speed (class 2/4/6)?
I'm asking because i haven't seen that happen, i have a class 6 4-gig microSDHC, and i rarely delete things from it, just slowly add more. And upon the time when it becomes too full, i'll pull everything, format it with Panasonics SD formatter (GREAT formatting program for SD cards of all sizes... but ONLY use it on SD cards lol), and replace all the files.