With a fix for 7142091 the original problem (setVisible(true) followed by an immediate call to setExtendedState()) is no longer reproducible - the extended state will be applied correctly (see the Description for a test case).
There's another problem however: we reset the extended state when a window is hidden, and re-apply it when it is shown. When a window is disposed, it's being hidden first. This causes the zoomed state to be reset, and as a result, an event is sent that notifies the application that the extended state is reset. Since Netbeans tracks the state of a window via the events, and preserves the state of a window based on the last event received, the maximized state of NetBeans window cannot be saved into a configuration file because when the window is destroyed, it is always restored back from the maximized state.