Have a b1550 tractor with 1640A loader.If you leave the loader raised I have found the next day or even a couple of hours that the bucket has lowered by itself (rear PTO does the same thing) Also if I have weight in the bucket raised and leave it for an hour or 2 it will tilt and dump on its own. Is this a control valve issue? If not what the heck is going on. I am A first time owner of this big of a tractor.