see here for the german source: http://videotreffpunkt.com/thread.php?threadid=8725&threadview=0&hilight=&hilightuser=0&page=1
He says (translated in english):
In GOP 4 the last original 'Pbb' group betwenn both b-Frames there is a b-Frame with size NULL. In the 6.GOP the last bb-Frames are missing and a new GOP structure with only 3 bbP groups starts: IbbPbbPbbP I... (the HF100 uses 4 Pbb groups)
Is someone here in the forum able to forward this information to technical guys from cyberlink?