TYPO3 Core

In TYPO3 6.1.29, under certain circumstances (I don't know which, it happens in one instance and in another it doesn't), the "new item" icon won't appear in the page module. AND there's no drag & dropping of content items.

In the instance with the error, I get this js error message:

Uncaught ReferenceError: Clickmenu is not defined
sysext/cms/layout/db_layout.php?id=10:167

Maybe it's the same issue as mentioned in this post:
http://www.typo3.net/forum/thematik/zeige/thema/115309/
http://translate.google.com/translate?hl=de&sl=de&tl=en&u=http%3A%2F%2Fwww.typo3.net%2Fforum%2Fthematik%2Fzeige%2Fthema%2F115309%2F

Also, the css hack proposed in that post does the trick, but of course won't make the js work.