The devs post/read on Battelog forums. On this site, we have Community Mangers.
http://battlelog.battlefield.com/bf4/forum/
You can also contact EA Help here:
https://help.ea.com/en/contact-us/new/
I suspect this is Engine related and probably affects Battlefront, Hardline and PvZ games as well (?)
I see. This is the settings page you changing it from? GPU Scaling Maintain Aspect?
If that's what you are trying.. perhaps try disabling Scaling and just set the game to 800x600 Fullscreen in the settings.
Most people have the opposite problem and I believe by default Scaling is not on at all.
*edit*
I did more googling and it seems this has been brought up before for both BF3/4 for people. The game sometimes seems to override the scaling options set by the GPU software.
One guy suggested to edit your PROF_SAVE_profile with Notepad (Documents folder)
GstRender.ResolutionHertz 0
Another idea I had was... set it to Windowed mode but use software to Lock the cursor it to the window so it doesn't jump off.
I use this software to lock to certain monitors for some games that refuse to lock it themselves:
http://dualmonitortool.sourceforge.net/swapscreen.html
I think it can do lock to Window too but I haven't test and I can't right at the minute.
*edit2*
After reviewing the settings for those tools.. I don't think those can do it but this software looks like it can. I haven't personally tested it.
even if i put the monitor on 800x600 and with black bars, still the game goes to streched
