Hey Matt_Cooke -
Great catch. There is indeed a bug with the vertex painting and the detail lighting mode in editor. I have alerted our engineers to it and hopefully we will get a fix in soon, but I don’t currently have a time table for it.
To clarify, the bug is after painting anything with vertex colors, the detail lighting viewmode will no longer render normals.
Thank You and I will keep you informed as we work on a solution.
Eric Ketchum