when using xbox controller for smart cam, default set up LB + A is being recognized as LB and A button click so engine increases in power.
This does not seem to be limited to just this keybinding. Other inputs that have dual inputs are also being recognized as two single input at the same time. eg Down pad plus X causes flaps to be lowered.
No, it works fine for me. Do you press those buttons simultaneously, or you press and hold LB and then A? Some skilled gamers push those combinations really fast, maybe you’re one of them? If it is a matter of speed, I’d bet that Asobo hasn’t thought about that 
Or maybe try to restore controller’s configuration to default settings?