The PiP seems bugged with configurations based on SLI. Indeed, screens and mirrors in the interior of vehicles suffer from a serious bug that make graphics flicker and flash and are simply unusable.

Here is a video of the bug (look from 1:19 and from 2:53): http://www.youtube.com/watch?feature=player_detailpage&v=pvZpUCUmJ1A#t=79s
http://www.youtube.com/watch?feature=player_detailpage&v=pvZpUCUmJ1A#t=173s

However, when I disable one of my 2 GPU, the bug disappears in the game and the PiP is working properly.
There seems to be an incompatibility between the PIP and solutions based on GPU SLI.