Well,
I'll be darned. Been towing for decades and have never, ever seen any version of any tow bar, that's extendable that is, that will lock in the retracted position. We've got lots of friends who tow Jeeps and all that and, there are several different makes and models of tow bars and not one of them will lock in the retracted position.
For one, as has been stated, in the retracted position, the distance is closed between the toad and coach. Depending on the width of the tow bar attachment on the toad, that could mean it's quite a bit closer to the coach in the retracted position. And two, the maker of the tow bar would have to make double locking mechanisms, IN and OUT and that would, I think, complicate things pretty good when, there is absolutely ZERO need for towing in a retracted position.
Scott