Is the PTO engaged by a cable, or a lever and mechanical linkage? PTO cables have a habit of getting stiff and rusty, and failing to move the shift lever through its full range of travel. Always keep a cable clean and well-lubricated. I very much prefer to use a shift lever to operate a PTO instead of a cable. The ones I have used frequently on dump trucks, heavy haul wreckers, and other similar equipment have a hinged lock plate to assure that the lever stays in the proper position, either engaged or disengaged. Umnless a PTO is specifically designed to run with the vehicle in motion, it can cause severe transmission damage if it's left partially or fully engaged.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!