There is a bug in Netbeans.
When running with Windows L&F, it seems there is a problem with class
com.sun.java.swing.plaf.windows.WindowsDesktopManager.

1) We had maximized JInternalFrame in JDesktopPane,
2) Then the JInternalFrame instance was removed (and then disposed) from JDesktopPane
3) Addin another instance of JInternalFrame into JDesktopPane and then selecting
it caused also a call JInternalFrame#setMaximum(false) on the first (removed) instance (!), what is wrong, causes problem for us.
The manager should release the referene when removed the JInternalFrame from the JDesktopPane.

See:
http://www.netbeans.org/issues/show_bug.cgi?id=22810