Kensington orbital scroll wheel two consecutive button press 5 when scrolling

Question

Using the scrolling function on my kensington orbital scroll wheel mouse in xev I see that two ButtonPress and ButtonRelease events of button 5 are triggered during a very small movement, followed by a long movement with no button pressing.

During normal usage, the use of the scroll wheel is very "jumpy" compared to other non-smooth scrolling wheels.

Here is the output from xinput:

Virtual core pointer                   id=2  [master pointer  (3)]
  ↳ Virtual core XTEST pointer         id=4  [slave  pointer  (2)]
  ↳ Primax Kensington Eagle Trackball  id=9  [slave  pointer  (2)]