Thanks for the video - I can see how this can drive anyone crazy - I'm sorry that you experience this :-(
IE is using a completely old school <textarea /> and a very simple client implementation which will explain that IE works ok.
As mentioned we are not able to repro this issue yet, so I will keep asking questions:
Are multiple users working on the same website simultaneously? If so, try editing ~/App_Data/Composite/Composite.config - locate the attribute broadcastConsoleElementChanges and change from 'true' to 'false' and restart site (Tools | Restart Server +
F5 browser) - then see if the problem goes away.
Are multiple users working on the same website and are they getting this issue as well? This could be a bug which is provoked by a some personal "keyboard tick" like "very quickly pressing left/right arrow keys, while thinking about what to
type now" etc. - if other people on your team are actively using the editor as well but are not experiencing this issue, try to notice if there is such a "tick" that can repro the issue.
Is the site publicly available? Would we be able to access and investigate on your site? If so, please mail me details; firstname.lastname@example.org
We are taking this issue pretty seriously since you have a clean install and experience it across multiple machines - but without a repro we are stuck.
We will soon release a beta build with Chrome support - this could be your salvation. Would you be interested in spending some time with this beta and Chrome and let us know if you are still experiencing the issue?
Thanks for helping us on this issue!