I have notied that it is not possible to have the same window-width on each lister in dualmode.
When exactly centering and updating setting it always moves a few pixel to the left or right after restart (tested with same columnsize on each side and also with different screen-resolutions). So for example left lister shows scroolbar while right lister has got 2-3 pixel space left before showing scroolbar.
When placing the divider more left or right from center the position is saved correctly. Same with metapane/preview.
As far as I can remember this never was in v9.