Are there exceptions to adding h parameters in feedback problems of amplifiers?

[dhruv.tara]

Homework Statement

In feedback problems of amplifiers we often use H feedback in the voltage controlled voltage sources... The good thing about that is that they are connected in series parallel form and they are then to find the net h parameters we simply add the h parameters of the amplifier (taken alone) to the h parameters of the feedback network (taken alone) respectively.

I was wondering if there are exceptions to this rule... I mean we connect the amplifier to the feedback network then isn't there a possibility that the individual parameters kind of change, maybe because of loading or something alike... Or is it impossible to happen. Can you give me some proofs?

Homework Equations

The Attempt at a Solution

 

[dhruv.tara]

someone reply please...