When a minecart with a shulker runs over an activator rail, the shulker is dispensed in a location where the shulker isn't able to attach. They exit just the same as any other mob.
When this occurs, the shulker starts to search for a valid block to teleport to and, especially when there isn't one or there are very few, creates lag.
I would expect a check for a valid block a shulker can stand on when exiting a minecart would occur. If none exists, the shulker should stay in the minecart.
This is a parity issue.
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Comments
GoldenHelmet
Xenon_177
It is still broken in 1.20.12
They even teleport onto trapdoors, buttons, rails and other redstone components
Xenon_177
they can teleport inside chests, water and even the block the minecart is on
migrated
They can also teleport onto half slabs
Confirmed: shulkers do not normally attach to non-solid blocks, but they can be put on one when ejected from a Minecart by an activator rail.
Steps to reproduce
Make a row of glass blocks > 20 blocks long.
Place rails on top of the glass blocks.
Toward one end of the rail line, replace a glass block with a redstone block and place an activator rail on top.
Set a stone block a few blocks off to the side of the redstone block.
On the other end of the rail line, replace a glass block with a stone block and spawn a shulker on it.
Place a minecart on the rail next to the shulker so that the minecart picks up the shulker, then place a rail on the stone block to reconnect the line.
Push the minecart down the line until it hits the activator rail.
Expected result
The shulker ejects and teleports instantly to the stone block.
Observed result
The shulker ejects onto a glass block, inside a rail, and then teleports to the stone block or the redstone block a few seconds later.