[blockquote]Then I would have expected a different solution from what you presented. Probably you should modify the printAllTagsAs() function rather than the search_quote() function. That way at least you will not have any side effects of the change.[/blockquote]
Someone else joined the discussion, the modification is not mine.
I thought the quotation marks in the URLS were the problem, but I was wrong, it was a magic_quotes issue. The URLS are working fine now with quotation marks.
My only problem now is that printAllTagsAs prints multiple-word-tags like:
`<...>"something something"`
This happend since I updated (from 1.4 to 1.4.1). Single-word-tags have no quotation marks, so the tagcloud looks a bit messy now.