I suspect this is the same as bug #880497 which arises from horizontal scrolling, as it is really easy to accidentally scroll horizontally while using two-finger scrolling. Could you check if that is the case?
Go into Mouse and Touchpad settings, and under Scrolling, select Two-finger scrolling and uncheck "Enable horizontal scrolling". Then try reproducing this bug.
I suspect this is the same as bug #880497 which arises from horizontal scrolling, as it is really easy to accidentally scroll horizontally while using two-finger scrolling. Could you check if that is the case?
Go into Mouse and Touchpad settings, and under Scrolling, select Two-finger scrolling and uncheck "Enable horizontal scrolling". Then try reproducing this bug.