Joystick roll axis is blocked while steering with mouse

[Tremzoff]

Hi, I am using mouse and joystick simultaneously. Mouse for pitch and yaw, joystick for rolling and drifting up/down. The problem: While steering with the mouse (pressing left button down) roll axis on my joystick is not responding. But any other axis on my joystick is working. After releasing left mouse button roll axis is working again. Any ideas?