If you have the top document view elements visible in the screen ie. free space at the bottom of the inspector( first picture). And you then scretch the pane large using the bottom edge you end up with a scroll bar for no apparent reason. (picture 2). But if you move it up even the slightest bit it goes away.(picture 3).
Created attachment 6574 [details]
A Window with free space in the top frame
Created attachment 6575 [details]
A Large window with a scroll bar for unknow reason.
Created attachment 6576 [details]
The Same Large Window slightly moved up so the scroll bar is gone.
This is fixed by my WebInspector branch.
This was fixed on the inspector branch and merged to trunk in r20986.