Horse takes damage (half a heart) every time you dismount. I have tested with removing all baubles, and moving location. Not sure the cause.

This isn't happening when I play. Can you send me a list of mods you're using? Or, better yet, see if it still happens without other mods installed?

Haven't been able to repro this due to the large number of mods, going to assume either it's a mod interaction or the ceiling is too low.

I know I'm mighty late, but I'm pretty sure this is caused by "Stupid Horse Stand Still"
I had the same problem and removing it seemed to work.