some space in the memory card is misallocated?

[Guest noct]

after using for a period of time, some storage space in the micro sd card seems to be missing.

say, when i select all files under /storagecard in file manager, they equal a total of 900mb.

when i go to settings/memory/storage card, it however shows 920mb of the memory card being used. 20 mb of space is missing.

The two numbers are consistent only after i formatted the microsd and copy back all the files onto it. From my ventured guess it could be when some files are deleted they are somehow not "freed" to the unused memory??? Is there anyway we can prevent this from happening?

i hate to format and put back the files everytime.

thanks