I've had the same problem. Checked again, and my speed is set at constant, so that doesn't seem to help.
Repro: Mac PB 15" 1.67 GHz PowerPC G4, 1GB RAM, OS X 10.4.7, Infinity USB-1 footpedal.
It's a real problem. Apparently no one from NCH actually monitors this forum?
-Gabe
London