[Rules] entering and exiting the mapboard

[JAN COLPAERT]

According to the rules units exiting the board may not re-enter play.

But an AFV Flamethrower may exit the map and replenish its supply. It must exit a friendly-controlled map edge however and remain off the map for six full turns. It can re-enter the map on the seventh turn and receive the modifier again.
Is this an exception to above rule then?