Two cameras. Both are live the whole comp timeline. The top camera is the "real" camera and the lower one is a temp one I use as a cockpit view when parented to various 3D objects. The bottom camera is always enabled but effectively not used due to layer order.
When I turn the top camera layer off, eye button, the viewer does not update to the cockpit camera. You have to move the playback cursor a frame to update the viewer.
The opposite works as expected. When enabling the top camera the viewer is instantly updated.
I was using this cockpit camera to quickly see; Am I pointing in the right direction.