This happens to me from time to time but rather when the winching force/cable tension is too big. Looks like a "feature" more than a bug. Just like some of the trees that are breaking when attached to.
Its not the same as that and I have tested it with more than one vehicle and attachment point. It also prevents vehicle to vehicle winching when either vehicle is near the boundary.
I can guess how this has happened. As a programming shortcut the same routines have been used for the new block post feature as originally used for map boundaries and in order that you can't cheat by towing a loaded truck through them the towing points are programmed to detach.