Another thought is , could the hose be breaking down internally, allowing flow in one direction, but not to return. Kind of like a check valve. Ive seen this happen on brake hoses, causes the brakes to stay on and not release the caliper.
Owned my x485 for almost 5 years now. Love the machine. The only nuisance is that grass keeps collecting on the upper portion of the mower deck around the belt/pulleys. I thought that I had read somewhere that there was a JD kit that added a lip to the front section of the mower deck to keep...