Noticed a very peculiar thing: when a camera is gouped and the parent group has non-zero transforms there are some differences in the render view from the viewport. i will look further into this, but I want to know if you guys noticed this too, maybe you know why it happens.
So, I found what is causing it and it was quite unexpected but logical:
there were some render layers and the camera was not assigned to any layer. Seems to me the transforms were ignored at rendertime.