Stability issues in a balanced amplifier

Hi

I try to build balansed amplifier. I use a transistor that has S22 above 1 without matching networks. I can't provide good output matching in single stage mode, hence S22 above 1 in this case too. But I can match all amplifier in 2 stage mode with coupler's help connecting it together. I want to ask:what is the cause of this situation? I think that the reflected wave from output load consumes on coupler's load. Can this produce instability of amplifier?


Thank you.