Hi axmiha,
the ability to do consecutive flights was added later in the run of our product - and it is a very complex procedure code-wise, resetting a lot of variables. It is also very hard to test, because obviously it takes a lot of time...
So it is quite possible that you discovered a hidden bug in our calculation, somewhere, probably unique to your situation.
We are planning to overhaul the whole VNAV calculation for a future update, especially to make the descent calculation more reliable. Therefore it would not much much sense to chase the quirk you encounter, as the whole architecture is going to change.
As a workaround I recommend to "reboot" gizmo after you park. Just click the little "flash" symbol on the right pop-out menu, then set up your plane again for the next flight.
As for your "turn around" mode problems, could you specify what you encounter?
Cheers, Jan