This is a new trouble to me.... not heard of it before. Here are some ideas...
1. Unplug midi cables, to elminate any stray feedback from the computer sequencer.

2. If you still have the problem, try turning off the 'DSP' effect (press the Blue DSP button, to turn it off)

3. If you still have trouble, try manually moving the pitch wheel...to see if it adds more bend, or has no effect. No effect would point to a bad unit (send in for repair...or if you are brave, open up the case, and remove the wires...one at a time....to see if the wheel is 'stuck' sending out a false message).

4. It could be possible to 'free up' the wheel...if it is stuck...by working it back and forth...while playing, to see if that brings it back to pitch

5. Press the Transpose button/ cursor down 1/ then right cursor to 'xx Bend' ...where the xx is the current bend setting. Change the setting to another number (using the yes/no buttons). The bigger the number, the stronger the wheel effect. Setting the number to '00' will disable the bend effect wheel.