There're no arrows to scroll so you can't resize the style-tab (only when swapping to another position). This appears on all resizeable buttons (placeholder, thumbnailsize,...).
Edit: This wasn't before. I think this bug came with 9.0.0.6 or 7.
Right Click and uncheck Full Width.
No, this is not activated, the sizes are always set to manual. When you swap the buttons and put a normal button to the end the arrows to scroll will appear.
Buttons set to full width are always as width as the button text!
Yes, I see the problem with Stile now.
Sorry, I can't duplicate this here. 
I think the arrows are not being seen.
If you restore the lister as NOT maximized, the lister can be resized wider than the screen size.
Perhaps it is a small bug, as this does not happen with 'normal' buttons.
I misunderstood.
I thought you meant the 'arrows' were the button resize handles, the little squares in the right corners .
Yes, of course you are correct.
The arrows to scroll past the right end of the lister are not appearing even though the button resize handles ( 'arrows' ) are not visible.