Mach speed/Stall warning test buttons problem

On my PMDG 737 NG, I have a problem with the Mach airspeed and Stall warning test buttons. Using the SDK events via FSUIPC, I have set up my physical push buttons for normal preflight testing. On pushing the buttons, the warning buzzer goes on as it should, but it refuses to stop. This applies to all 4 buttons, and it doesn't matter which parameter I use, it keeps doing the same thing. When I go to the overhead in the sim, the buttons are showing as released. I have to then push the buttons with the mouse cursor, to silence them. The L/E devices and Wing overheat test buttons behave as they should with no problems. I just cannot figure out what is causing this issue.

Cheers.