Clicking on window title bar to minimize it
I'm running OS 10.13.3 on a new 5K iMac.
In System Preferences > Dock I have checked the setting for putting a window into the dock when double-clicking on its title bar, which is the way I like things. However, I´ve just discovered quite by accident this does not work with iTunes (12.7.3). This seems odd, as iTunes is an Apple app. I know I can minimize it by clicking the yellow button, but that´s not the way I would like it to work! Is this a bug? If not, why is iTunes apparently excluded from "normal" OS behaviour? Or is there some relevant .plist file or whatever that I can delete? Thanks for any help/suggestions! Ian