I reported this earlier and it got closed because I think it wasn't a clear description. I'm not talking about turning grass to path when there's a block above it. I think this is better explained in steps-

Steps to reproduce:
1. Place down a grass block
2. Next to the grass block, place down any normal block (I used logs)
3. On top of the normal block, place down another normal block
4. Place a button on the side facing the grass block of the normal block placed in step 3
5. Try changing the grass block to path. (won't work)
6. Remove button and convert grass block to path
7. Replace button (path stays)

I don't think this is intended behavior because when you replace the button, the path block stays as path and isn't converted to dirt. I think you should be able to change the grass to path with a button adjacent, or that the button changes the path to dirt.