Windows 7 x64, Quadro 4000
Broken: 2.77a, 2.78 any build so far
Short description of error
I've made a demo file to test. In this file there are three scenes. If you switch from Scene to Scene.001, and then directly after that hit the Tilde key (which calls bpy.ops.view3d.layers()), the active render camera is removed from the slot.
Exact steps for others to reproduce the error
Open the provided Blend, switch to Scene.001, hit Tilde. The Scene.camera property becomes None: