I'm confused. I just called up a MIDI track, and "N" turned snap on and off. When I turned it on in the PRV and went back to Track view, it was still on and audio clips could be quantized. When I turned it off in Track View, it turned off in the PRV. If I had different snap amounts enabled in the Control Bar and in the PRV, the settings remained as set when turning snap on and off with the "N" key (or using the Snap on/off button in the toolbar).
I am not experiencing Snap persisting in the PRV after turning off Snap. I can even have the Track View and PRV open at the same time, and turn snap on or off to turn it on or off in both tracks simultaneously. I'm using X3e, you're using X3d. Think that could be the difference?