@Mateusz Konieczny: Small addition/idea: Maybe you could set up a second (recurring) bot that changes the cases surface=paving_stones + material=* to surface=paving_stones + paving_stones:material=*, or removes material=* if material=XYZ AND paving_stones :material=XYZ are set (and the values are the same)? And who sets a fixme or note if the 2 values are different?

This special case with the material at surface=paving_stones isn't very pretty...