Ok, no responses forthcoming, I guess I'm the only one hit by this.
Anyway, did a "quick" and dirty test.
Installed Zentyal 2.0.3 on a virtual machine disconnected from the internet, set up Zarafa and a user. New mail works as expected, the html-formatting buttons are where they're supposed to be.
Then connected the machine to internet, updated the Zentyal-components, which btw. did not contain any zarafa-updates. Rebooted the machine, html-mail still worked.
Then ran apt-get update and apt-get dist-upgrade which did mention zarafa webaccess-ajax and zarafa-webaccess-mobile. Rebooted. After restart, new html-mail fails to show any formatting-buttons, html-mail has in effect, disappeared.
Soo.... I guess this update messed up Zarafa's config-files or perhaps something even more important.
Will try to find a reasonably old-config file in a backup and see if that solves anything.
I guess the lesson learned is to stay clear of community updates to Zarafa.
::Trym