When using lenses, results not including the quoted keywords are returned.
Reproducing
My original query was for TTi instruments "PL303QMT" but in order to test the default search behaviour I've used the following query that includes a non-existing word : unquoted words "astrolopicat"
- Search for unquoted words "astrolopicat"
- Turn Forum lens and search again
several results are returned, with approximations of the quoted word
So, it seams like it defaults to the "searching for X instead" style of search instead.
this open issue about search in Videos might be related.
I think the correct behaviour should be to return no results, as I think you do, since that is the behaviour I see when the lens is off.