When a sign is placed on a block and is above a grass block, you cannot turn the grass block into a path block.
Additionally, when a sign is placed on a block and would be above a path block, it reverts the path block to a dirt block
Environment
Windows 10 v1909, Java 1.8.0_201 64bit, CPU R7 3700X, GPU Vega 56, driver Radeon 20.1.4
Thank you for your report!
We're actually already tracking this issue in MC-84731, so I resolved and linked this ticket as a duplicate.
However, that ticket has already been resolved. That means that this is not considered a bug and won't be fixed. Please do not leave a comment on the linked ticket.
If you haven't already, you might like to make use of the search feature in the future to see if the issue has already been reported.
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