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Ah, yes, there seems to have been a bug with billboarding for armature bones - I just fixed that, please download the zip again from github and reinstall plugin + restart blender, it should work now. Let me know if you have any more problems. Just as you know, though, i can't promise that the model you import will come out exactly the same way if you re-export it. Mainly because materials are handled very differently in my exporter (and there is no common intermediate format for this).

Thanks, it's working now. I used 'Remove Doubles' to reduce vertex count on a model then exported it as MDL, but the number of vertices in the exported file is the number before 'Remove Doubles' was used. Do you know why that happens?

Yes, each vertex can only have one normal and one UV coordinate, so if you use sharp normals or have a UV seam, then the vertices will be split in two at that point. Most 3D formats work this way.

Ah I understand that now. Many thanks.