This problem is not an hardware problem of the real switches connected to the switch jumper on mainboard.

Seems that it is an software problem that OS X calls an shutdown that does in real an restart.
Some part of DSDT may be involved but i dont know which part.

Also the problem isnt an problem only of those newest mainbords & Snow Leo special, i also seen that problem in insanely forum for complete different (older) mainboards & 10.5 also. Not an very often problem , but know i think.

I would search the (at this time much bigger) insanely forum for that shutdown restart switched problem.