1. Open a demo: https://jsfiddle.net/fpua774e/
1. Try to select any part in "Try to select some text" text. It's preferable to make a selection horizontally, e.g. from left to right (vertical scroll should not be triggered at all in this case).
Text is selected.
Browser goes crazy with vertical scrolling.
I'll just add that CKEditor customers reported this bug to us, and it's a critical bug that makes using CKEditor impossible in Safari (see http://dev.ckeditor.com/ticket/14314).
Does this still happen in nightly builds?
I can check it on Monday, as currently I don't have any mac nearby. Nonetheless you can always check it in demo that I've attached.
Checked just with the latest nightly, and it's not fixed.
This seems to be fixed in 9.1 which is in the 10.11.4 betas.