Assistant: Searching non-existing term with filters turned on, returns all pages

When searching for junk (something that doesn't exist, e.g. "asdflk;j") and filters are being used, the search results will show every page. (or so it seems like every page of the filter)

This doesn't occur when the documentation is "unfiltered". It properly returns "Your search did not match any documents."

To Repro:

1) Open Assistant from the Qt install
2) If you don't have any documentation showing, add a document.
3) If you don't have Filters Toolbar, enable it. (View->Toolbars->Filter Toolbar)
4) Select a filter for the documentation.
5) Try searching for something that doesn't match anything. (e.g. "Ajlk;jkal;sa;j")
6) You should get a lot of hits.

See attached screenshot.