Still I find the non interchangeability between FP1 and FP2 not satisfying.
Summary of my problem: I have bad sound which becomes normal if the one call button is pressed.
IF only ground and mic pins are inersed between OMTP and CTIA and IF the call button connects these two pins it makes all sense to hear perfect sound during button is pressed.
And this supports my claim, that FP1 uses different standard as FP2, which is my main point of disappointment in terms of sustainability…