Matt, the turn signals were the problem. I couldn't be entirely sure that the weight of the bags resting on the turn signals wouldn't bend the stalks, so I flipped them. It bothered me at first because the bags are obviously optimized for the other orientation (not least because the water bottle holder is now at the rear). But I'll get used to it.
In practice ill never have a passenger while the bags are on -- the simplest symmetrical way to secure the bags is to strap them to the foot pegs anyway -- so this is all academic.