It is very possible.
You need to check what the landscape issues as the channel it responds to after you make the change.
Its very possible that in-spite of what you have it set to the physical material is taking over for it.
And its even more possible that after 4.22 - in which the engine landacape was bugged and not returning a physmat at all - some id1ot thought it was a good idea to hard code a default response.
If you want to bypass it, you can pull the engine source, fix it, and maybe even go as far as pushing to the repo for inclusion.
You’d sooner be dead if you were to wait for Epic to do anything about anything.