Recently, i have a problem related to mass storage mode - after doing several tests i am able to reproduce this behavior every time:

After restart to the N900, i connect it in mass storage mode, and both mmc and mydocs becomes accessible from my pc.

after i disconnect from mass storage mode and reconnect again, only MyDocs is available and i get this message:

"Only device storage connected, Memory card already in use"

I am unable to access mmc card again in mass storage mode until i restart (it is accessible from the n900 after i disconnect mass storage and not accessible after it is connected again - so it seems that the mass storage mode actually dismounts the card, but still i cannot access it from the pc).

Anyone knows how to debug/fix this issue?