Can someone explain to me why, once airborne, if I try to engage the spoilers they will arm but if I try to push them further to apply drag for slowing down during descent they will initially raise but then the handle, as well as the speed brakes themselves, will lower on their own to the arm position. I am using FSUIPC (registered) and can raise them fully while on the ground but not in the air. Any ideas?

You are probably better off asking this in the PMDG forum