Based on a forumpost at OcWorkBench, rumors have appeared that Crossfire won't work properly in combination with Intel's new P45 chipset. It is said that while testing with the Catalyst 8.4 drivers, the screen deforms.

As reported here earlier, the first P45 motherboards are expected in five weeks. The chipset does not support nVidia's SLI chipset, leaving Crossfire as multi-GPU technology. 

Since these are only rumors, there is no certainty on the problem yet. BIOS and driver incompatibility have been suggested. When this is the case, it's quite possible there will be updates shortly after the introduction of these new motherboards.