This is coming in Shader Forge 2

Was it originally created in a very old version of SF?
It could also be that you're using some invalid character in a comment somewhere

Oh, you need to connect the MIP input of the texture for that to work on OpenGL. Undocumented thing that should throw a warning.

What if you set it to only have a single light source rather than multiple ones?
And what if you disconnect diffuse and set the shader to unlit?

Yes, the window that pops up should say which texture it is at the bottom, whenever you select something in it. The currently assigned texture should be highlighted by default

When you press select, a window pops up, and then if you highlight the texture, it should say somewhere in the texture selection window

I guess you could click select on the node, and then look at the name of the texture, and then search your project?
Anyhow, this isn't really a feature request, closing it :)

This probably won't make it into SF1, but SF2 should have support for multi-pass shaders, where you can specify exactly what each pass should do

The lightmapping system is going to be rewritten for the next update, so it should be fixed pretty soon