Hmmm, I never see a scrollbar. Maybe the easiest workaround would be a mode where the user can disable all automatic sizing (possibly after getting a good initial setting), and then use the user's size choices? That's the behaviour you get on Mac (and MSWin) and something I more or less expect everywhere. I often deal with files that have long names for which I don't want the required width to be allocated - and iin general I strongly believe that the user should at least feel in control of his GUI (there's a reason I don't use Gnome ;)) Dialog information is already saved so there should be no need to implement something new for that.
I'm currently a bit handicapped by the recent requirement bump to Qt 5.10 (which is not supported on my main machine and I thus don't have on my Linux rig either). I'm slowly working my way around that but kio still a little way off.
