I would say it is normal. If you look at the geometry of the boom cylinder, you will notice that it doesn't take much movement of the cylinder to drop the boom by quite a bit.
I always keep the boom and swing locking pins in place on my BX23 except when using the BH. However, a while back I left the boom pin out just to see what would happen. Over a period of several days the boom dropped enough that the bucket almost touched the floor.
My BH bucket "uncurls" a couple of inches overnight, and my stabilizers drop maybe a quarter to a half inch. I always try to keep the FEL on the ground when parked, so I can't comment about drift on that end.