I've been loading my saved games to find out which one this message comes from, my game files have just been copied from my original clean unmodded stock game files and I've replayed the mission.
As you can see its appeared again.
Any other bright ideas chaps because I haven't got one, it's June 5th 1945 and when this campaign is over with I'm going to uninstall everything and re-start it at the beginning of 1945, then we'll see if this anomaly can be repeated.