I wonder where the CG location as a percent of mac is on each of these Caps especially the original airplane in question.

But the bottom line is that a lot of airplanes with the same planform and tail moments arms that don't have the difference in vertical positioning don't have the problem.

It has to be something that effects pitching moments. Since similar wings don't have a problem like this then you are stuck with the horizontal tail. Keep in mind that the moment change required is very very small.

I doubt it is a stall of the horizontal tail since the flow would seem to be seperating and reattaching awfully easily.

Those of you with Caps and are familiar with the flight path angles and are good at estimating the angles of attack need to do a little arm waving at the airplane and estimate where the wing wake is going.

The thing about a configuration with the wing and tail in relatively the same vertical position is that the tail is almost always in the wing wake except for high alpha maneuvers.