Um,
Does the 139 AFCS have SAS, ATT modes similar in concept to the Sperry system as used on the 212/412/76 families of helicopters? Those Modes were "Un-coupled" but greatly added Stability to the Aircraft especially when the Attitude Mode was engaged. Depressing the Cyclic Trim Release acted to over ride the Attitude Hold and allowed a new reference datum to be created.
SAS and ATT worked at all airspeeds. I would be surprised if the 139 system works much different.