it was just the turn I gave the order
I re-tried in SP: normally all one click -> ship order is set and deleted
-> just try all
with double clicks - sometimes after selecting e.g. a colony ship "select a ship"-Windows closes, sometimes not).
- normally a double click to e.g. colony ship selects it AND closes the window
- sometimes the window stays (as already Iceman wrote)
however: in SP i had now no crash, and in MP it caused the crash (I hope nothing else was the reason

)