I have two NSWindowControllers setup both from XIBs I want one of them to show up as a sheet on a different window made from a different XIB. The problem comes when I call NSApplication's beginSheet:modalForWindow: modalDelegate:didEndSelector:contextInfo: function one of those two window controllers i mentioned before will show up as a sheet as you'd expect. The other one doesn't. It shows up in the initial location that is defined in the xib, without the bar at the top with the close button. what causes a window to come on as a sheet and not be connected to the window?