As of NetBeans 7.1 non-document windows in the same docking spot are organized into a tab group and are no longer stretched by default. To support this new feature SyntheticaAddons V1.6.2 provides an updated NetBeans plugin. The new plugin is backwards compatible and works fine with NetBeans 6.9/7.0.
To enable the old appearance/behavior NetBeans supports the system property winsys.stretching_view_tabs. By setting the system property to true you can force NetBeans using the old streched tabs appearance.