editor erratic behavior

Hi
I tried searching for similar threads but could not find one. The problem is with visual editor. The error repeats regularly on its own. I cannot cause it myself it just happens: sometimes I delete text say 2 paragraph. then scroll down to 4 or 5 paragraph and continue typing there (not using copy or paste). Then when I scroll back to the top the previously deleted paragraph is magically in its place.
Sometimes editor does it with couple of words and/or half sentences.
This make the writing process very slow and difficult because you need to double check everything many times.
First I thought it was caused by W3TC object cache – I disabled it. But the same error is still happening. I do not have any other plugins.
It fees obvious that some kind of cache is causing this but I cannot identify which.
Another cause that I am thinking about is keyboard – maybe it has a shortcut to undo?
let me know if anybody else has experienced similar issue and what was the fix.