we run a multisite with 3.9 and since the visual editor is broken.
there is no usable textarea anymore and the button are completely missing.
touching the resize corner results in a sudden disapearence of the "white blank space".
We have disabled ALL plugins without any change. we also purged the cache, restarted the php-fpm and the webserver itself. no change at all.
wed like to encourage you to roll back your changes at the visual editor so ppl can use it again.