Can't close throttle

I am using a Project Airbus A320 on my sim, the throttles are connected through a USB interface card and set up in AST. This combination has been working fine in FS9. In FSX, however, I cannot close the throttles on the sim to idle. If I press and hold the F1 key the power reduces to idle. If I let the key go the throttle opens again even though the cockpit lever is at idle. Something is opening the throttle in FSX. I have the joysticks disabled and FSUIPC is not processing the throttles. Anyone any idea where this is coming from?
Barry
www.a320sim.com