Dock Icons

Since I upgraded to Mountain Lion something very annoying is happening to me. When I minimize my apps they do not minimize into their respective Icons??? They were before the upgarde, I checked in Dock Preferences and i have the radio checked for Minimize windows into application icon but this is not happening.

Any advice would be greatly appreciated. This is actually happening on my Mac Mini as well as my Macbook Pro since the update. I have tried unchecking rebooting and checking again as well.

Thank you very much