At a guess, you are seeing an irrelevant message relating to one of the secondary storage controllers. As well as the six SATA ports provided by the Intel Z68 chip set, there are two ports provided by a Marvell 9182 and another two (eSATA) by a JMicron JMB362. I suspect the message is coming from the Marvell controller.
I don't think it's rebooting - I think it's showing the splash screen, interrupted by the appearance of the Marvell message, restores the splash, shows the discovery of the drive, etc.
You could disable the Marvell controller and see if that gets rid of the message.