just a simply idea.
As you know, it,s not possible to make MAT files for props.
In same cases (prop with one group) it may be a solution to convert a prop into a figure first (and simply rename the figure to pp2 and move to props to have it on the right place).

I checked it with a simple prop, making a phi with only one group and converted it and MATs are possible now.

What do you think about?

Robert