In the Vehicle Showcase, I went inside the Hunter GMG, and then hopped into the Gunner's seat.
Instead of using the PIP, I decided to change to full-screen remote control of the weapon. I then hopped into the Driver's Seat. This broke the FOV, and it was as if my view was zoomed in - pressing, holding ot tapping the +/- on the NUMPAD didn't change the zoom. This was only fixed by changing back to the Gunner's Seat, with the PIP remote-control of the weapon (Without going fullscreen) - and then back to the Driver's Seat.
PS: If you jump out of the vehicle when the bug happens, your view will still be zoomed, but you will be able to zoom out with the appropriate key-binds.
Attached image shows the zoomed-in view. {F16767}