KB Article: http://support.microsoft.com/kb/2732814
Application isolation is a new printing feature in Windows 8 and in Windows Server 2012. This feature isolates applications from print drivers so that applications do not crash if a print driver crashes.
Application isolation makes every application that interacts with a printer driver more stable.
In Windows 8 or in Windows Server 2012, a printer driver that is running in isolation from applications may not have full functionality. For example, watermarks do not print correctly.