As an ex display driver on the A4 (way ex), I recall fondly (not) the assymetric slat extension we got on that aeroplane.
While the roll tendancy was easily enough controllable, there definitely was a roll tendancy. This would suggest a lift change between "in " and "out" - whether this was due to more lift on the extended side, or the lift vector moving outboard, I don't know.
I, too, would be interested to hear more on the topic from an aerody guy.