When searching in the XMLUI Item Mapper, multiple words (with a space in between) always returns no results.
It seems like it could be an encoding problem, as inserting a plus symbol in place of a space will return results.
So, for example:
A search on "my topic" (no quotes) will always return no results (even if there are matches). But, a search on "my+topic" (no quotes) will return the correct number of results.