PC,
yep...could be, but I'm not sure whether the suction of a running engine is needed to create this phenomena.
I'm not even sure if this actually is the explanation..........I just can't think of anything else.
To be honest, I know I have a creative imagination, but I would never have predicted this effect (if it's true) to continue for this long.
I think that the boys and girls from Donauwerth might have addressed the "couple of minutes" note in the ASB a little further.
I was about to shut down the thing after more than 10 minutes wittnessing the Main tank qty go down, thinking I must have done something wrong.
Still, I'm almost certain now that this is exactly what happens.