SAU Stabilize - is it reversed?

When you turn it on the 21 becomes very floppy and when you turn it off it flies like it's on rails.

Shouldn't it be the other way round?

I don't know about floppy but stabilization should require more stick travel for the same result. The airplane will be more sluggish or lethargic.

With the AFCS engaged in the STABILIZATION mode, control of the aircraft does not differ from that with the AFCS not engaged, except the fact that the stick forces and travels required to build up identical roll rates or g-loads are somewhat higher.

During performance of aerobatics and conduct of dog fighting with the AFCS engaged in STABILIZATION mode, the control stick forces in the pitch channel increase substantially, thus hampering piloting or the aircraft. So provision is made in the AFCS design for disengaging the pitch channel only, by placing the AFCS, PITCH switch to the OFF position; then the roll channel stabilization will be retained.

As for overshoots of roll reversals it's seen clearly the difference between stab. off and on. It is probably the case that the damping and filtering of stab. has not been adequately tuned and possible the aerodynamic model doesn't have the negative behavior that stabilization would justify

Stab-off should be very difficult or not impossible to snap from -90 to +90 bank without overshoot and oscillation. Square wave input into pitch or roll should have distinct negative result to the point that it makes sense to design and build some kind of stabilization filter (like Ka-50 which is more difficult to control with raw input).

It seems that the current stab. mode simply drains down control inputs at a reduced rate compared to not which is going to feel wallowy.

When I disable the stabilize mode pitch channel I see no difference vs with it on. I would guess it should work the way pitch does with stabilize off.

Yes, SAU pitch channel off switch disables pitch input during the stabilized mode only. All other pitch input works the same regardless of switch position (automatic landing, climb from dangerous altitude, recover to level flight).

The stabilize mode pitch stick movement resistance was found to be disruptive to combat-type flight. The stick required much further travel for the same result.