Using a 27-inch iMac ( Mid 2011) or later as an external display

I recently purchased a MacBook Pro Retina and am trying to use a 27-inch iMac (Mid 2011) as a display for the MacBook through a Thunderbolt cable. I have both Mountian Lion and Windows 7 (Bootcamp) partitioned on the MacBook and Mountian Lion installed on the iMac and both work perfectly.

When I reboot the MacBook into the OSX side of the harddrive and have the Thunderbolt cable attached to both the MacBook and the iMac, I am able to use COMMAND -F2 (known as Target Display Mode) to switch the iMac to display the MacBook screen easily.

When I reboot the MacBook into the Windows side of the harddrive and have the Thunderbolt cable attached to both computers, I am NOT able to use COMMAND-F2 to switch the iMac to display the MacBook screen.

Why isn't Target Display Mode not working on the Windows 7 side of the harddrive? Do I need to install more drivers for the Thunderbolt port for the Windows 7?

Any help would be appreciated.

Thanks!