UE5.6 Auto landscape material bug

In UE5.6, creating an auto material and adding it to a landscape, then painting another layer over the auto material causes the compoment next to it to have black spots painted on it.

I tested in a blank project and it does the same, but I upgraded from 5.1, to 5.6.

Does anyone know if there is something i am missing in the new version, or is this just a bug?