Items fail to remain on surface

The bug

Items will repeatedly float to the surface then glitch to be 3-4 blocks below, and resume floating to the surface.

How to reproduce

1. Go above kelp (all the times I've tried it it has only happened above and in kelp)
2. Throw out a variety of items
   → Some will float normally, while some glitch downwards, sometimes once they have reached the surface, sometimes under the water