Bug.
When fishing, a large percentage or xp orbs are not collected by the player. They will fly away from the player.
Xp orbs can be collected by swimming over to them, and are absorbed normally.

Expected gameplay.
100% of xp orbs absorbed by player.

Actual gameplay.
Majority of observations burst out away from player. Some are still collected.
The amount collected continues to mend the fishing rod with mending to full health.
There are not enough xp orbs lost to affect the durability of the mending fishing rod.

To replicate.
Use a fishing rod (mending, lure III, luck of the sea III, unbreaking III).
Build a platform at sea level.
Use the fishing rod as intended to catch fish and items.
Watch the xp orbs float away.