Output-pane scrollbar

Hi all,

I'm using two output panes that are combined together (ie are linked
together for scrolling vertically).
This is done by having one using the :without-bar keyword.

The trouble appears when one of this output pane has a horizontal scrollbar,
and the other doesn't. Then they do not share anymore the same height, and
maintaining their scroll positions at the same place seems difficult.

So here is the question: is it possible to constraint an output-pane so that
a scrollbar is always visible ? Which keyword ?

thanks,
Sebastien

PS: LWW 4.2.7