Junus,
up to now you didn`t tell us about the load capacitor.
Knowing this, I have the following comments:
* The additional circuitry (you call it "pos. feedback") enhances the transconductance and, thus, the overall gain. This is the desired and expected effect.
* At the same time the output resistance certainly will be effected - but I don`t know in which way. However, this modified output resistance - together with the capacitive load - will change the phase response of the whole circuit. Thus, no surprise.
* More than that, I think this additional "pos. feedback" cannot be compared with the "normal" pos. feedback (and it´s consequences) as known, for example, from opamps in the voltage feedback mode.
* That means: It is clear that the gain as well as the phase response is effected by the additional circuitry - however, I am not able to give further detailed explanations without time consuming additional investigations.
I am afraid, that´s all one can say - unless somebody has gained already some experience with this circuit.