This also occurs in 4.14.3
This does not occur on Windows.
Could not get this issue to reproduce while recording the screen with quicktime player, but if you experience it in person it really feels off. Confirmed by another iMac user.
Using a logitech G100s mouse.
Repro 1: Orthographic views
Note: this also mildly affects vertex painting, although the effect is much less noticeable.
Repro 2: Landscape:
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-40767 in the post.