This has been discussed a lot. They are going to be working on ALL the camera issues. http://www.beamng.com/threads/1182-Proposed-Camera-Changes
For now, try to look up with camera, when it is under the terraind keep moving your mouse in the same direction unitl it will... change the direction and then the camera is not inverted in Y axis If you don't understand I can record a video for you
Instead of having it be inverted or not, please let there be an option to choose. I am one of those people that uses the inverted controls on the Y axis, so this feels natural to me.