Putting a shulker in a minecart causes the to glitch.
To replicate:
Place a minecart track facing towards the shulker
Push a minecart into the shulker
Move the shulker aroud and observer glitch
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Can confirm. It's also impossible to break the minecart with a Shulker in it, but that may be because of the large hitbox.
Edit: Also, when you take a screenshot, it snaps to one position.