The text datablock was linked to the controller. So even if the script was set to 'module' and saved, once linked/appended the object the script would come together.
If someone wants to implement this "clear" only once the file is saved, please go ahead. But I believe it's ok to loose the script if you change it for module (and with the new datablock lookup it's straightforward/quick to reassign a textblock)
-- bug not reported anywhere, from my own list