As is, NEWT WindowImpl performs requested operation regardless whether the native implementation supports it. Here, the Window's stateMask is also modified regardless of successful operation. Hence stateMask reflect the 'attempted operation' instead of the real state. 'getSupportedStateMask()' provides knowledge about supported operations, as introduced via Bug 1188. We may refine operations, i.e. not performing operations and allow stateMask to reflect the real state.
cc00d9b6c5a5c6b71ba14311fc6b17ce932d9a1e Bug 1208 - NEWT: Window: Consider avoiding operations if not supported, see getSupportedStateMask() - Skip operation if not supported - Fix skip operation if isFullscreen() && !isNativeValid(): We have to store the state w/o action, so the state can be picked up at native creation.