The Fullscreen property does not work properly with input values. For both banshee as VLC CanSetFullscreen gives true while playing video, Fullscreen gives True if Fullscreen and False if not, as supposed. But if you want to set fullscreen by passing True it fails to do so in both the players I tested, from fullscreen to windowed works.
This is an implementation issue with those players, so you will need to file bugs on their bug trackers.
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