Is that 8600 an On-Board, PCI or PCI-E version?
I ask, because the 8600 chipset is available as an Integrated Graphics Controller (IE: Part of the motherboard, not a separate card) so it might help to clarify which of the three we are dealing with.
Also, if it is an Addon card, who is the Vendor? (eVGA, BFG, etc?). If On-Board, on what motherboard?
Answers to these will either deepen the mystery or answer some questions, but these posts might fare better in the support thread if it turns out not being specifically an issue with RC2, so do you have other Nightly Builds that this behaviour also happens on?