PTO Momentarily engages when clutch is let out

[Clevelandtx]

I have a Farmtrac 360DTC, 39HP with 400 hours. I don't understand how this can happen so I sure could use some advice. It has an electric three position PTO engagement switch (OFF, Independent and Manual) that works properly in all 3 positions. The issue is that with the PTO Switch in the OFF position and I let the clutch out, the PTO mysteriously engages for a moment. Enough to spin up whatever is hooked up and then goes back off and functions properly until the next time the clutch is let out. Some background, not sure how it may be related. This all started happening after I had the synchronizer, forward and reverse gears replaced. The repair shop said they had no idea. I am sure it is related to the repair but just don't understand what the problem could be. Any advice or knowledge of how this could possibly happen is greatly appreciated.