I'm wondering if your seeing results of the rear end doing some steering. !st, you have an issue when decel at 65 with it hunting for a line. Then you have to correct in mid turn because your getting more turning input then your giving the car. Both would indicate the rear end causing your unwanted destabilization.

Have you tried bumping it into neutral when you decel to see if the condition still exists? If the rear is experiencing a change in toe as it travels through the suspension travel, you could get both experiences you have. Maybe your bump steer is coming from the rear canted 4 link. Wouldn't take much of a bind or side movement to cause an uneasy feeling for the driver. A minor wheelbase change as the rear suspension articulates could cause your issues as well. Gene