Skywatcher enhanced dual axis handset. RA problem.

[warpout]

I have a Skywatcher dual axis set up( RA and DEC motors with the red enhanced handset) Skywatcher 200P on an EQ5 Mount. Tracking is great with very little drift. The problem is that after an hour or two when I try to slew in RA the motor just keeps running even though I've taken my thumb off the button, so I have to disconnect the power to stop it. When I reconnect the power the motor resumes normal tracking, until I press the button again. It doesn't matter what the speed setting is(0.5x, 2x, or 16x) it runs at 16x. It's the same in both directions. This only seems to happen after I have been using the controller for a while. There is no problem with the DEC axis. I Use a Celestron Power Tank. HELP!