It’s because you’re adding the texture to itself, you actually want to mask it with a ‘component mask’ node and make sure that R, G and B is checked. However what you’re doing right now is creating a single scalar value which is R, G and B combined, NOT a Vector3.
Using the white output of a texture shouldn’t give you RGBA though, that’s just RGB combined. What’s the rest of the material network like? It sounds like there’s an error with the material elsewhere in the network. You can multiply a scalar by anything, but not a Vector3 (well you can, but not without errors).
Also, emissive materials do not receive ANY lighting information. The lighting in your model above hasn’t flipped, it’s just the information from the texture.