by yvan vander sanden.
I got a similar problem. Well, the same actually. And it's not only TinyMCE, but also the file uploader doesn't load when in editing mode.
It seems to me some javascript modules are not loaded in this case. No idea why though.
Possibly related:
If I use the assignment upgrade helper and try to select multiple assignements to upgrade, then click 'upgrade selected assignments', i get a message telling me nothing is selected. (see image below)
I recently upgraded from 2.0 to 2.5, one version at a time. The site did seem to work on each step, but of course I didn't check every feature...