Users, who tried to install and use mnoGoSearch TYPO3 extension could see two ghost items in the plugin's flexform configuration. Here is how it looks like:
I was sure that it is not a problem of the extension. So I took a deeper look and discovered a TYPO3 bug: TYPO3 will show ghost items in the multiple select control if that control has default values. However if you save the item, ghosts will magically materialize. Funny!
It is the first time I saw ghosts in TYPO3. Not very scary, heh?