Comment 5 for bug 1828080

@Seth: what is the right reaction to a horizontal scrollwheel? Horizontal pan?

I've pushed the attached fix to master/5.1, so at least middle-mouse panning can work as "normal" for 2D scrolling mice (interpreting as a vertical scroll -> zoom is certainly not helpful, IMO).

Adding extra handling to the axis == 1 case can be added on top.