Although it could just be some kind of bug, I assume rather that this is some type of marketing strategy -- deliberately sabotaging the product. In which case, its a poor strategy.
Its to be expected that TCDX wouldn't have all the tools for making 3D objects. But what isn't expected is that the 3D objects it produces are second-rate, lame-duck objects. TCDX already has enough bugs and gotchas without deliberately introducing more.
Waiting until the tail end of a process to see what the rendered version is going to look like sucks the fun out of the project.
The "drag material from the palette" technique doesn't seem to work for me. Is there something I need to do to the tcsurface object before it will take? When I drag the material, it doesn't select a facet, or do anything to show that its willing to apply the material to the object.
One workaround for the "once only" defect is to save the part you're working on as an in-place block just before you apply the material. Then explode the block back to itself (tcsurface) and apply the material. When you need to modify the part some more, you can delete the part, copy the block back in place, explode it back to a tcsurface, make your changes, save as a block again, explode, apply material. Phew.