Thanks for your answer. You are right this could be the problem. I will try it out in the near future.

cheers,
Mathias

And now your key handler function runs and sets a control variable (global) then conditions its further action on this variable.
In the meantime you run a second instance of the "same" function which suspends the first one and now this second instance of the function changes the values of your variables (global) which after the end of this instance of the function will still be used by the previously called function. Alternatively, the action of this second function will be determined by what variables were changed by the first function call.

You can check at the very beginning of the function if the variable is_running (example name) is True, if so, exit the function. Then you set is_running to true, then your code and at the very end of your code in the function you set is_running to false. Then next execution of this function during previous one will break it.

Something like this

# initial value of semafor
# put below line at begining
# of your program
is_running = False


# put this inside your function
if is_running:
    return
else:
    is_running = True
    # insert
    # your code
    # here
    is running = False