Join Date: Feb 2010
Location: Loudoun County, VA
I've had a couple horses that want to lay down with me and I've seen it happen to others. It's usually horses that have just started their training. They aren't used to be worked, they get sweaty, it feels different with you and the saddle on them, so they want to roll because rolling feels nice on their itchy backs. Just encourage your horse to move, they get used to the feeling, and they don't really try it much more.
I'm surprised your vet or your farrier didn't say anything about this... I thought it was fairly common.