Mobs that stand on a hopper and then killed drops XP orbs that are stuck on top of the hopper.

After disconnecting and reconnecting the game, those orbs cause a weird behaviour. An infinite flow of XP orbs jumping off the hoppers in pulses and absorbed into the player but has no effect on the XP level.

This weird behaviour stops when I jump one block above the hopper and the stuck orbs are released from the hopper.