I think that some of this phenomena is a symptom that the "Handing Over/Taking Over Control" has never been taught and practised properly in the first place.
I find it is quite a common experience that pilots have little or no response to the "I have/you have control". This should have been taught and practised from lesson one.
I am not ex military but have instructed for the military and they are much more pedantic on this issue - perhaps an indication that they fly more to the limits when it is vital that the student relinquishes the controls when he hears "I have control".
Also bear in mind that most modern training aircraft are side by side seating so its possible to elbow the student if you have to - not so easy in a tandem aicraft.
That said in circa 5,000 hrs instruction I have never had a student "freeze" on the controls although I suppose there is always a first time!