Hey whyman - that is strange, I don't believe I have seen that issue before.
In the panel on the right-hand side where the model previews are, does the model show as black there, or does it appear correct there and just not in the map?
Also, if you are able to, could you zip up your game folder (or at least the "maps" and "tiles" folder) and send me so I can take a look at it?