Kelp and sea grass grows up into flowing water and makes it a source block

The bug

Kelp and sea grass (when bone meal is used) can grow into flowing water blocks, not just sources, and as a byproduct of that, the flowing water becomes a source block.

How to reproduce

1. Create a water column of source blocks, with flowing water at the top
2. Place kelp at the bottom and watch it grow (bumping up random tick speed if needed)
3. Observe the flowing water at the top is now a source block. (destroying the top kelp and using a bucket or debug screen can confirm this)

Code analysis

Code analysis by [Mod] Avoma can be found in this comment.