Since Microsoft has introduced the new UI (previously called Metro) with Windows 8 and Windows Server 2012, you can not start multiple instance of a same program if you launch it using Metro.
- From session opened on Windows 8 (or Windows Server 2012), hit the Windows key to make Metro appears
- Type notepad
- Windows finds Notepad and you can launch it by hitting Enter key or click on the result
- Notepad is launched >> Ok, fine
- Now, repeat the previous operation
- Windows returns to the previous instance
- Now, try using the Run command (Windows+R), you can start as many instance as you want using the Run command
What a mess !!!!!