I am just guessing here, so don't hold me to this. Is the deck level when it is in the 'raised' position? I don't know how they do the leveling on that unit, but on some they are only level once they hit the stops. My Deere LT was like this. I just cranked the leveling knob all the way up, then cut. Not that it would hurt anything, it would just give an unlevel cut.
...the more I think about the G's. Maybe it is because when it is 'raised' the hydroulics are holding it up, and bouncing around cutting grass is putting strain on the system, not to mention it may gradually drop as your cutting.
Dont quote me. Just thinking outloud.
-Ben