Problem with img_assist class not inserted for textarea (in editor)

Suddenly I lost the image-assist popup links under my textareas and tracked it down to the fact that the class 'img_assist' isn't inserted into the textarea-tag.

I can't however track down the reason for this. I've tried to change the settings to work on any path and all textareas without any change.

I get no javascript or server errors. The js-function Drupal.behaviors.img_assist runs, but finds no textarea with class 'img_assist'.

It worked for a while after installation, then after a while it stopped...

It's working on my local installation using the same versions, so it's a bit hard to try to track down.

Any hints as to where to look are most appreciated!!

Image assist 6.x-2.0-alpha4
Drupal 6.13