^{Update by Mega_Spud:}
Summary:
Grass Path blocks turn grass blocks below them to dirt, but grass can still spread to these, thus creating a loop of grass/dirt blocks. Blocks below grass paths should stay as dirt.

Steps to Reproduce:

1. Open a standard flat world
2. Place grass blocks on top of other grass blocks
3. Use a shovel to turn the placed blocks into grass path blocks
4. Increase the random tick speed (eg /gamerule randomtickspeed 500)
5. Watch the blocks underneath the path blocks

Observed Results:
The blocks underneath the path blocks alternate between grass and dirt blocks repeatedly.

Expected Results:
Blocks below grass path blocks should turn to dirt blocks when ticked, and remain that way. (As per MCPE-19203)

Screenshots/Videos attached: Yes
grass_path.mp4

Notes:

Original Description:

I noticed the grass path blocks created with shovels don't seem to prevent the growth of grass blocks placed underneath them, which as you can imagine results in some pretty gruesome visuals. I attempted to replace these submerged grass blocks with dirt, but the grass grew back before long.

I suspected it was probably an issue with the grass path being less than a full block in height, so I tested it out with some other semi-solid blocks with similar results.