The round had just started. I had the engineer kit and put down some mines north of the flag. Then I did some running around and found an abandoned German vehicle (the 250). I drove around for a little while, got on the gun for a couple of seconds, then drove around some more and got on the gun again (I think switched from F1 to F2 to F3) and voila, le crash.
I haven't been on my game pc since then so haven't tried to reproduce it yet.