Thanks for your help.
I defined my own set of keys in a dedicated KB profile, but even when I revert back to the DEFAULT KB profile the F keys you are referring to do not work as expected, only F5 and F8 work as intended (Full down/Up) but the One notch keys do nothing.
It is strange though that I don't see issue with other aircraft, I tried the
C152, the Bonanza and the Piper Cub (the Cub having a 'real' handle in stead of electrical activation like the C172 and the Bonanza), all these are working fine.
I ended up now assigning two PB's on my warthog throttle unit, one for flaps down and one for Up, this seems to work OK.
Still don't understand why the KB keys are not working correctly though.