I'm using WordPress 4.0 on an IIS installation.
Everything is working fine, execept for one thing. My editor wrote an article and saved it. When page refreshed the visual editor become blank, without the content (I've checked that the text wasn't white).
Then I've checked the problem and made a re-save of the article from phpmyadmin. Then the content of the article appeared again, but at first save from WP it become blank.
Last case: if I set to use the "Text Mode" of the Editor, I don't have problems, article is saved correctly and refreshing the page I can see its content.
PS: already tried to disable all plugins and use the default theme.