I must be missing something obvious but here’s my problem. I have a model with a couple of materials. I select linked by material, go to uv editing and start unwrapping and laying out my uv’s for texture mapping. So far so good. Works just fine. Then I take the next step and I want to add a second uv map for light mapping. I can use the plus button to add a UVmap in the object data properties section but I the fail completely at making changes to only the second UV map.
I tried deselecting all, then clicking on the second uv map in the properties section to highlight it. Then select all vertices and mark the all as seam. Unwrap with margin (all of which works fine by the way) but I find that my first UV map has also been changed and all of the hard work of making sure all the face are aligned along the right U or V axis would have been lost if I not had a backup.
Again, seems so basic to me that it is probably staring me in the face but I can’t see it.