When riding a horse that is sinking in water, if you try to jump, the horse will rear up (stand on its hind legs) as part of the normal jumping animation — but then the animation becomes stuck. The horse continues to move around with the "rearing" pose frozen in place.
The animation glitch is fixed when you mount the horse again.
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We are tracking this issue in MC-97423, so this ticket is being resolved and linked as a duplicate.
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