I'm talking about the "tx_wood" bug. It occurs when you install Bloodmoon: The add-on introduces a new ingredient, "Heartwood", which can be obtained from dead Spriggans. The ingredient's model uses the "tx_wood.tga" texture, whereas the vanilla Telvanni models make use of the "tx_wood.dds" texture. Since Morrowind does not distinguish between texture file types but rather looks at the files' names only, "tx_wood.tga" replaces the .dds file. This leads to the weird observations I erroneously thought to be the result of wrong behaviour on OpenMW's side: OpenMW: Differences in handling UV maps compared to vanilla Morrowind.
To cut a long story short: If you want to use the correct textures on your Telvanni exterior models, you have to extract the original tx_wood.dds file from your Morrowind.bsa -- e.g., by using the BSA Unpacker MW -- and place it in your Data Files\Textures directory. The downside of this solution is that the Heartwood model will look different now (see below). To fully solve the issue you'd have to extract the .dds file, rename it, and apply the renamed texture to the Telvanni .nif files (you could do the same with the .tga file instead but keep in mind that you'd have to extract the .dds file to your Textures directory anyway.)
- Heartwood after extracting the .dds file.
- Heartwood with Bloodmoon texture.
