When UI status and/or navigation bars are disabled with

main() {
    SystemChrome.setEnabledSystemUIOverlays([]);
    runApp(...);
}

Opening the on-screen keyboard (eg, tapping on a textfield) re-enables the UI overlays (all the appropriate padding and everything is added on).

The UI overlays remain enabled even if the keyboard is closed until the app loses+regains focus (eg, putting phone to sleep and turning back on or switching to different app and switching back). After the reload, the overlays are off again.

It is reasonable to provide the navigation bars on Android when the keyboard appears because the back button is required to close it, but the bar should go back to being hidden after the keyboard is closed.