stuck on tractor PTO shaft - removal?

My brother was using a 50" rototiller behind his Ford NAA, and when done tilling the garden, he attempted to unhook the PTO shaft from the tractor PTO stub shaft. We can depress the release button on the PTO coupling, but can't pull the shaft off the short stub shaft. You can push the shaft forward, and then back, but it appears that the release spring/pin is not aligning in a way to allow the PTO coupling to slide off the shaft.

Does anyone have a quick and easy way to rectify this situation? Do we need to drive out the latch pin from the PTO coupling to release it from the shaft, or has some stress on that coupling (from running tiller) caused the shaft, latch pin or something else to mushroom or deform so it can't be removed?

We've tried depressing the latch pin with a pin punch to the bottom of the travel, pushing it foward and re-releasing it, but nothing will budge the PTO coupling off that tractor stub shaft.

Thanks for ideas - we hate to pull the PTO shaft out of the tractor to rectify this situation.

The pin should have a groove all the way round it so if it's clearing to go forward there could be dirt built up in the shaft so the shaft won't shorten up to come off.

You should be able to push the stay pin all the way inwards against the spring and on the back side pull the lock ring off and push the stay pin forwards completely out of the coupler.