I have many saddled horses, with and without armor, and I cannot control them now. All you can do is make them jump.
EDIT: Now after a few minutes they respond.
EDIT 2: I restarted my server and the issue happens again. It seems that after a few minutes they will be controlable, but not after the server first starts.
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duplicates
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Confirmed, Although donkeys are still controllable.

Duplicate of MC-16182
When I get this problem I can look around and the horse copies as it's supposed to when it's controlable, but not able to walk, though jump. Solution is to either try with another horse and then go back to the problematic one, or go interact with something else and it might work again.
EDIT: As I just noticed, it seems like it has to do with the full screen mode, or at least it caused my horse to go from controlable to not by switching fullscreen on with F11. Don't think this problem occurs in the Options environment though, as I guess it's safer for the system.
Though I'm using windows 7.
it seems that when you log of and back on again the horses don't respond anymore. as if the game forgets they have a saddle equiped