I'm with Mephiston on this one - you can leave OWing fms on OW without an activation roll only if it/they are your last activations and you choose to end your turn. Seems pretty simple to me and the benefit of staying on OW without a roll is balanced out by losing the use of that activation. Still, given how many holes there are in the rules, you could probably spend all of eternity debating it one way or another.

. . . . . And we did
But that is what was decided.

So potentially a formation could garrison thus starting the game on OW, and if it does not activate or use the OW for turns #1 and #2, it could carry its OW through to turn #3.