When items are pushed upwards due to being inside a block, they can get stuck in a situation where they should be pushed out to the side.
In the clip and screenshot, the item stack is mostly in the water stream but has an X coordinate decimal > .875 or < .125, so it is also partially in the glass block alongside the water stream. Its Y is lower than the ceiling on the water stream, so there should not be anything stopping it from being pushed out of those glass blocks and fully into the water. Instead it is bounced back and forth between the two glass blocks on the side of the stream along the Z coordinate and does not return to normal physics behavior without breaking the blocks.
Reproduced by shearing a sheep that is fully encased with blocks, but can probably be done with an encased dropper/dispenser as well.
Environment
Java 1.8.0_51 64bit
Windows 10
Linked issues
is duplicated by 6
MC-255891
item entities partially inside blocks not get repelled in the correct direction and glitch around
Resolved
MC-300708
Items that are located in a place where a shelf is going to be placed start moving until someone breaks the shelf or the item gets collected
Resolved
MC-302594
Item/Shelf Glitch
Resolved
MC-304479
Item Entity Stuck in Wall
Resolved
MC-306531
Dropped Steak is acting weirdly
Resolved
Attachments
Comments 3
I found it also happens when placing a shelf over a block that is in the ground and there is another shelf where the item is supposed to be pushed out. There is a video of it in MC-300708. Can confirm it happens in 26.2
Can confirm in 1.16.5.