Component.removeNotify unconditionally hides the peer object before calling
dispose() on it. In the case of a modal dialog which has already been hidden,
this can cause an assertion failure under java_g int AwtDialog::WmEndModal.

    ASSERT( ::IsWindowVisible( GetHWnd() ) );

Instead of unconditionally hiding the Dialog, Component.removeNotify should
test the Dialog's "visible" flag before calling peer.hide().