PWM Signal disturbed by write access to Port A

Hello everybody,

i am currently working on the generation of PWM signals with an ATTiny84 and Timer0.
Thereby I came across a very strange problem:
The PWM signal is cleanly output at the OC0B pin (PA7).
But as soon as you write to any pin of port A, the PWM signal is strongly interfered.
This only happens with pins on port A.
Any write access to pins of port B does not influence the PWM signal.
Is this a real problem with ATTiny84 or does it only occur in SimulIDE?
What could be the cause?

Philip

Bug confirmed. I'm working on it.

Thanks for reporting.