I finally got the footage. Here you can see Vettel passing Kobayashi under yellow lights. It must have happened between lap 14 and lap 16. To me there still remain some mysteries.
In lap 8 Vettel was behind Kobayashi, wanted to overtake but stepped back because of yellow flags. Then KOB pitted and was way behind afterwards.
[youtube]http://www.youtube.com/watch?v=3CN9uVivqyo[/youtube]
In lap 16 VET passed KOB in regular move. Then SKY showed the replay with the ominous pass.
[youtube]http://www.youtube.com/watch?v=_CjaWDa9ZRA[/youtube]
The race lap chart shows that both were in between range from laps 14–16. So VET must have passed KOB at the end of lap 14 or 15 and immediately let him pass again before crossing the start-finish-line, otherwise the timetable would have shown the pass.
So, were it yellow flags? It's not quite clear and there are hints that it was just yellow lights due to slippery surface, because there were no marshals waving yellow flags and there was no incident that would legitimate yellow flags.
From lap 8 on the red and yellow striped flags were shown due to slippery surface.
[youtube]http://www.youtube.com/watch?v=fzRszjivccE[/youtube]