How to reproduce:

1. Open attached project
2. Open scene main.unity
- Scene contains some cubes and two cameras. One camera renders the UI and the other camera renders the 3D space. The 3D camera is disabled, but its rendering is called through a script, using Camera.Render()
3. Play the scene
4. Open the Profiler window
- Note how there is only a small number of Draw Calls in the Rendering profiler
5. Enable the Camera Component in the 3D-Camera gameobject
- Note how there is now a huge amount of Draw Calls shown