Mmm..playing devil's advocate here but wouldn't the turns onto course and then the vibration of the engines cause the fuel mix to stay mixed?
Like bushy, I am also aware of the 210 crash in Central Australia. The story I was told was that the pilot misfueled the aircraft from drum stock while doing a mail run. The engine started running rough almost immediately on starting. The pilot shut down and phoned the engineers who advised remaining where he was but he thought he would travel another sector (for what reason I have no idea). The engine seized (I think) forcing a landing into scrub.
