Suppose you have a warrior character with x swordfighting skill. You change his class to priest, and you are no longer able to know what your skills are. When you change back to warrior again, does he/she have a detoriated swordfighting skill or again have to start from that lousy 5%?
Skills don't get deleted, so aside from deterioration, your skill will still be there later.
Thanks Tom for the fast reply.