I rode a horse into water, it worked fine until it got 3 blocks deep, then I fell off as expected, but even when the horse came back to 1 deep water, right-clicking would only jerk the camera angle, not get on the horse.
After that whenever I tried to place a block, it would only work if there was a previously destroyed block in that same space, and would turn back into that block the moment I placed any block there.
Mobs also seemed to act normal, except it was impossible to interact with them, and they didn't notice me at all.
It fixed itself when I /killed myself, but I didn't try to reproduce the bug again.
Everything was the same when I switched between Creative and Survival, except in Survival I got the block I placed back.
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Was it all mobs or just zombies? cause I had a similar issue where zombies ignored me but spiders attacked.
I am having the same issue. Also if you go into f5 mode you are floating above the ground, sitting. lol
This is me floating above the ground like I am sitting on the horse but I can't interact with anything. Happened when I tried to ride in the water. Also I cant hold spacebar to float in the water.
What I discovered about this is, if you drop items, they drop where the mounting bug had occurred, as if the player was still in the water. If you fly up high in creative, then switch to survival, you won't take fall damage. This is because the game thinks you are in the water where the glitch occurred. You can't place/break stuff because Minecraft detects where the block was placed, checks to see if it was even possible to break/place that block based on where you are standing and how far your gamemode allows you to reach (distance calculation), and "shoots down" any packet suspected of a block place/break hack.
If you place/break blocks within reach distance of the spot you glitched out, it should break/place just fine.
All the above is just a theory based on my experience with this bug. If anyone would like to prove my theory, please, do so.
This does happen and is annoying.