If the game is minimized so that a PBEM save is added from e-mail to the save directory, RUS crashes upon return, error message referring to "burst mode".
This is unique only to the situations when something is added to the save directory - minimizing, restoring in other cases works fine.
Unfortunately I cannot find this in any of the logs, but the situation is easy to recreate - minimize, add a new file / directory to the save area, try to restore.