FBWB trouble with throttle

Hi guys, please help me.

I use Arduplane firmware v3.9.2.

I think that Fly-By-Wire mode B does not work correctly. Last time I tried to turn it in air, throttle just turned into minimum and didn’t reacted on throttle stick. I did some experiments on the ground to recognize the cause of problem, but I was not successful. I just blew into the tube that was connected to the airspeed sensor. Mission planner shows that airspeed increased, but throttle value has not changed at all (returns minimal value like in flight before). I tried to disconnect GPS sensor and change some parameters, but result remained the same. Is this just a bug? I need to know how I can check FBWB mode on the ground.