How to use the tab strip?

Hello,
I have a problem with the tab strip: the line that is drawn to separate the tabs and the navigation window (where I place the tabs) ends “somewhere”. It does not start at the top of the window and doesnt go down until the end. Since resolutions are different on different screens the navigation window (docked) vary in lenght, so I cant just put an extra line above or adjust the object size…

I hope you understand my problem, anyway I took a sceenshot where you can see the problem.