Readjusting the clock fixes the problem for his current session, but every time he reboots, the clock automatically readjusts itself based on the time zone setting.

Essentially, the incorrect clock setting happens because OS X and Linux use GMT time while Windows tries to synchronize with your local time zone, getting confused when you reboot between the two.

Causes of Time Discrepancies Computer clocks can diverge from the proper time for many reasons. Setting your clock to the wrong time zone forces it to synchronize with an incorrect time reference.

So if your computer’s clock is in the past, it may think that every message it receives is spam. Many standalone devices also have a built-in clock, which are frequently wrong as well.

If your company's computer clocks aren't in sync, forensics, backups, and much more can suffer. Simson Garfinkel on getting the time right.