User blog comment:Kirkburn/Technical Update: January 6, 2015/@comment-5558012-20150106183750/@comment-126761-20150106201141

We do know of the scrolling issue - it's definitely on our list, but I don't have an ETA for the fix at the moment.

The issue can occur when you have the classic editor's visual mode enabled, and switch from it to source mode (or when it falls back to source mode automagically).