At some time in the A6 to A7 shifting phase there existed a statement from JCL in AUM magazine (I believe) that he imagined to have the complete light and shadowing part of Gamestudio being performed by a shader pipeline.

So it makes sense to me that there are two materials for "classic" block rendering (from WMB style levels) - one shader for "flat" surfaces and one for lightmapped surfaces (just because you have the precalculated lighting information).

At least I would do so if I were to integrate lightmapped content into my rendering pipeline to blend it with dynamic lights and shadows.

I would be careful, if I were you - maybe the shader code is written just for shaded block with assumptions you don't know. At least I would assume that there is a texture lookup and a lightmap lookup, using the second UV set, which was generated by the WMP lightmapper.

I did a search for mtl_shaded in the engine code, but there is just the MATERIAL* pointer, hence I think it is set by the engine. To understand what it is beneath, I would try to dump the content of the char* effect, void* d3deffect or void* d3dmaterial pointers.

However I would say it is a waste of time - if it works for you - go with it.