I've implemented the behavior of "scroll the field down while the user is holding something selected" before, and my initial implementation had this bug, so I think I can explain a likely reason this happens. My code listened to mouse movement events, and if a selection was present and the mouse was moved into the top or bottom regions of the scrollable area, then the area would scroll a bit, and a recurring timer for some number of milliseconds would be started (if already active, then it would be reset) which would case the area to scroll a bit more. (This timer would be canceled if the mouse was moved out of the auto-scroll region.) If you continually moved the mouse, then it's possible the application would get the mouse movement events at a higher rate than the timer would fire, so the scrollable area would scroll faster. I think I found out that the platform would emit the mouse movement events at up to 60fps, so I just tweaked the timer to match that. Not a perfect solution, maybe I'll update it eventually to check the system time and scroll slower if the mouse move events are arriving faster than the timer.