Hello Candy
If you are using tabbedContainer style (see
http://4js.com/online_documentation/fjs-fgl-manual-html/#fgl-topics/r_fgl_presentation_styles_window_style_attributes.html), it will work as you expect. The startMenu will replace the side bar and will be resizable.
In your sample, you are using a normal window. Then the sidebar is resizable and the startmenu is not. I added GBC-1809 for this request. I let you communicate your time frame constraints to your support center.
Olivier Imbert.