Can't use minus and equals to control mixture?

[moeburn]

Was having a heck of a time controlling engines manually.  I had changed the keybinds so that minus and equals control mixture, not throttle like default, because I already had throttle on my joystick throttle axis.

 

I just assumed that when minus and equals then did nothing, it meant the planes had no mixture controls.

 

Nope, turns out my keybinds did nothing.  Even reassigning them back and forth did not get it working.  The only way I could get mixture controls to work was to assign it to anything else other than minus and equals.

 

But there's no little orange square indicator saying "minus and equals are already assigned to some other key", and they're definitely not anyway. 

 

I just can't use these keys at all unless they are set to control throttle it seems.

[JimTM]

I just tried minus and equals in the P-40 and it worked OK with mixture. I needed to temporarily delete my existing mixture bind to an axis on my CH Quadrant to get the keyboard binds to work though. Do you have any other binds for your mixture besides minus and equals? 

[Youtch]

For some plane like Tempest, Spit V and Mosquito, it looks as if the only binding that works for mixture is if it is an axis and not buttons nor key.

 

Is it normal?