Confirmed in 15w51b.
Oh darn. So that guy's going to respawn every night?
I'm in survival with cheats disabled, but I'll try to use NBTExplorer right now. But I know it's not just a glitch with tags, since you can't make a Skeleton float without having it riding something.
Hmm. Didn't find that one when I searched for "horse".
This has been around forever. I thought it was just a design decision! 😛