I’m having the same issue using WP 3.5.3 and ACF 4.2.2. There are no JS errors that I can see through dev tools or FireBug.
It may be worth mentioning that just last week I experienced a conflict with WPMU Dev’s Whitelabel WP Videos plugin causing ACF wysiwyg field buttons to go missing (defaulting to HTML view) without Chrome or FireBug complaining about any JS errors.
(sidenote: it wasn’t actually the WPMUDev plugin itself; more precisely it was the fact that I had them enabled in the “Help” pulldown tab of the admin area).
That is where I am going to start looking as I try to figure this out.
Thanks for a super addition to WP!
