Every time I attempt to use a lead on a zombie or skeleton horse, (Yes, I've tried it in creative) it makes me sit on the mount instead of the intended action. I have tried restarting my computer, restarting the game, uninstalling and reinstalling Minecraft, all with no luck at fixing the bug. This bug has already been posted on this site, but it was NOT resolved as it might say:
https://bugs.mojang.com/browse/MC-16898?jql=text%20~%20%22Leashes%20cant%20be%20put%20on%20undead%20horses%22

Which is why I'm reposting essentially the same thing. (It hasn't been fixed.)