Has anyone else experienced a sudden, random rackspace change while playing a Pianoteq instrument in Gig Performer? If so, what did you do to correct the problem?

Typically, this can when (a) you have a button, slider, expression pedal, etc mapped to GP that is intended to switch rackspaces and then (b) the controller sends such messages out randomly (obviously a fault in the controller or possibly wiring). GP itself will not switch rackspaces on its own - something has to trigger such a switch.

(Disclaimer, I'm one of the GP developers)