WoW!
I wanted to give you some karma but got the answer: "You must spread some Reputation around before giving it to DaltonST again."
As I have no automatic tags from Zotero (I turned this feature off to have full control on my tags) I wanted to copy all my imported ZManual Tags to the Calibre Standards Tags. But the format #zotero_manual_tags:tags did not work as this feature is only for custom columns. So I had to create a custom column as you suggested in the tool tip.
Just a minor think: It would be nice if ZMI could remember place and size of the ZMI window.