this link?
http://support.microsoft.com/kb/315231/en-us

The other you provided just brings up a search page.

Can we be clear about this problem? When you say Log-off, do you mean the same as "Shut down" the computer? EG, Start > "Turn off the computer", then in the Shutdown screen you select Shutdown, instead of Restart or Standby.

Or do you literally mean "Log off" from the Start menu?

If you mean Log off from the Start menu, what do you expect to happen? I ask, because it seems to me that if you have selected automatic Log on, then as soon as you log off, the system will automatically log you back on.

If you mean Shut down, then does the computer shut down but then immediately reboots, (restarts), itself? If so, then this would appear to be a different problem like WOL, or Wake-on-Lan where a LAN or Local Area Network is waking up the computer. That would be a setting in the BIOS.

What was the application you installed where this changed?

Mark