When you, or any entity, fires an arrow and it hits bamboo  if you log out before the arrow despawns when you log back in the arrow has a blue potion effect on it and no longer despawns ever.

I have a ton of them around my base on the realm i play in, and its easy to reproduce.

plant some bamboo, fire an arrow into them, log out. Logging back in the arrows should have blue particle effects and never despawn.

I think the arrows become the uncraftable tipped arrows?