rod03801: understood. I might actually go for the solution proposed below by 'cookie monster' (I thought it is 'vegetable monster' now??), because I'm afraid someone is willing to put the effort in to find my starting position from last game and track my moves and gain a significant advantage.
(not that it would be needed at my current level of play - you can still win easily against me if you know a bit what you do)

rod03801: yes that works, but I would have to overwrite or save the changed position every time. It should work without that, right? And the really strange thing isthat it seems to work, but the game comes back to me blank after several hours only.

Chaos: I mean that I move two or three pieces around, for example take two out and place them switched. I typically do that, so opponents cannot check earlier games to see whee my headquarters is.

Anyone aware of this problem?
1. I load an existing saved position
2. I modify it slightly
3. I submit my move
Everything looks good, the game is shown as it is my opponents turn.
But - some hours later - the game is back in my list, with no position, and I have to do it all over again! I have tried five times for one game, I cannot get it to work. It always comes back to me after some hours with no position.