when entering the end, after dropping items into it, the game will start to lag. The Items will stack up after some ticks. Right after entering there are ~13.000 entities. After some waiting, the items will still be there, but as 64 items stacks.

to reproduce:
throw many 1x stacks in the end
open f3 menu -> many entities
wait 3 minutes of lag
items will be there but stacked