Were you on a runway when you exited? You must be on a runway, taxiway, or the rearm pad when you exit, or else it is a ditch. Simply taxi back onto one of the above if you happen to roll off during landing. Simply landing within the field boundaries is not enough.
If you were on a runway, then I have no idea. I don't think anyone has every reported a problem with ditches messages while on a runway.
-Soda
The Assassins.