Serious issues with multiple vessels in space simultaneously

[RabidSmurf]

Have a vessel in a stable orbit around Mun, go back to KSC, go to VAB build a plane, fly, crash revert to VAB. Suddenly Mun music in the VAB. Try to load plane on runway again, game locks up and crashes.

Reload, Mun music in VAB again, go to KSC/tracking center check Mun mission, previously stable orbit now shows a collision course with Mun, take control, see the fuel tank is empty, was the engine firing while I was testing my plane?