If I use any project that has the player’s mouse visible and I eject to use the camera, the mouse will allow me to rotate but the mouse is locked to the play window and you can tell when it hits the edge and the camera stops rotating. The only way around is either by making the cursor invisible before ejecting, or by releasing the mouse and clicking again every so often when trying to rotate to keep the mouse in the window.
I saw that this was supposedly fixed (UE-29313) before but I am still getting the bug in 4.16.2 from the launcher.