It would be serious, if it were actually the case that the server, properly configured, was rebooting due to a remote scan. However, Occam's Razor would suggest that since one of the primary goals of server design is reliability and a port scan (even one as thourough as a complete nmap scan) is a fairly innocuous event, that the cause is not a bug, or at least not unintentional.
I would very carefully go over your hardware setup, and the configuration of the server. I would run the offending scan many times, altering different things to try and determine some predictable behaviors, and I would go over the server logs to see if the reason for the reboot was logged. Cheers, nate > This is serious, whether or not the -O options was used is > not so relevant; it certainly should not cause the machine > to reboot.
