This seems to be a bug in Windows that can be fixed by doing the following:
- Click on the Start Menu
- Type: Screen saver
- Click on "Change Screen Saver"
- Choose any Screen Saver from the drop down.
- Change the "Wait" time to 30 minutes.
- Change Screen Saver back to "(None)"
- Click "OK" at the bottom.
Your screen should now only lock after 30 minutes as it's supposed to.