Why is NSWindow's sharingType not being honoured when in fullscreen mode

When I set the NSWindow's sharingtype to .none and then test the content accessibility by taking a screenshot, the screenshot is not allowed by the system (as expected)

NSApplication.shared().mainWindow?.sharingType = .none

After the application switches to fullscreen:

self.view.enterFullScreenMode(NSScreen.main()!, withOptions: [.default])

When testing screenshots again, the system now allows screenshots, which means the window's content is accessible to other processes, which should not be the case.