Even though nothing can happen, I'd separate them for the time being. Even unshod hooves can leave a mark and Bay could potentially get hurt.
Well, for the moment I've let them all out into the big pasture. There's better grass coming in out there and it's keeping all their minds otherwise occupied ;~D
Cyn's the one with a few marks on her rear, but nothing serious.
I don't really have a setup that is good for ~keeping~ them separated on a regular basis, so I am sortof hoping this has been tried once and learned from ;~D