Bug confirmed, I'll fix this for the next release.
> Btw. maybe the duplicate check could be possible for the second (answer)
> field too?
At the moment, the philosophy behind 'find duplicate questions' is to find the duplicate questions, so that you are never in a situation where there is ambiguity if there is a question.
Feel free to open a uservoice request for your feature request, though, so that I can see how popular this is.
Cheers,
Peter