ZDoom

fixed

		if (i == 1 && texture1)
		{
			// The very first texture is just a dummy. Copy its dimensions to texture 0.
			// It still needs to be created in case someone uses it by name.
			offset = LONG(directory[0]);
			const maptexture_t *tex = (const maptexture_t *)((const BYTE *)maptex + offset);
			FDummyTexture *tex0 = static_cast<FDummyTexture *>(Textures[0].Texture);
			tex0->SetSize (SAFESHORT(tex->width), SAFESHORT(tex->height));
		}

			offset = LONG(directory[1]);

After experiencing some odd situations in Memento Mori 2 which needs this compatibility flag in a few maps I looked at all the code involved.

Then I found this in FTextureManager::AddTexturesLump:

[code]
if (i == 1 && texture1)
{
// The very first texture is just a dummy. Copy its dimensions to texture 0.
// It still needs to be created in case someone uses it by name.
offset = LONG(directory[0]);
const maptexture_t *tex = (const maptexture_t *)((const BYTE *)maptex + offset);
FDummyTexture *tex0 = static_cast<FDummyTexture *>(Textures[0].Texture);
tex0->SetSize (SAFESHORT(tex->width), SAFESHORT(tex->height));
}
[/code]

It reads the number of textures in the TEXTURE1 lump and treats it as the offset to the first texture. Result: Some random value gets set as height of texture 0 which breaks the compatibility flag.

It should be:

[code]
offset = LONG(directory[1]);
[/code]