Hi welcome back.
Yeh, the mipmapping in TR and in OpenGlide are different. The setting in TR causes it to generate mipmaps (copies of the same texture, but at many different resolutions). It passes them to OpenGlide via the Glide interface, but OpenGlide ignores them. The setting in OpenGLid.INI causes OpenGLide to generate its own mipmaps, from the base texture that TR passes.
Texture capture only grabs the base texture, so you don't get to see TR's mipmaps, however the mipmapping process seems to make a slight difference to the base texture, so what you capture looks very slightly different. Also, since the folder names are derived from the texture contents, you end up capturing textures in different folders.
I see what you mean about making mipmap=high res, but I don't have a strong oppinion ether way. I think if pushed for an oppinion, I'd go for normal=high res, because that way fresh installs of TR would find high-res enabled, giving one less thing to confuse users. In any case, I think mainly people would do the on/off thing with F4, where they can't see which state its in.
Did you get a chance to try the new Glide.exe I left for you, BTW?