Tall seagrass or kelp growing when underneath flowing water turns the flowing water into source water

Discovered while testing a similar, recently-fixed bug which I also could not find.

To reproduce:

1. Create the setup shown.

2. Use bone meal on the seagrass.

The flowing water block above the seagrass will now be a full water block.

Ideally, either the bone meal should not work at all, or the block on top should remain flowing water while still containing top-half seagrass.