If you want the old stricter Google behavior be sure to check the "Verbatim" option under 'tools', or add "&tbs=li:1" to your uri.
Around 2008 Google started testing a new search engine logic, codenamed caffeine?, which eventually became the default. Without being sure, I think verbatim uses the old engine which wasn't trying to be smarter than you and your query, certainly is stricter and reminds the old Google a lot.
True. Aware of verbatim, though oddly forget and assume “quoted” text is verbatim. Personally I would perfect Google provide option to have verbatim on by default and enable non-verbatim per keyword; obviously average user would not like that.
EDIT: Tested if verbatim flag fixed the issue above, it did not; Google still randomly returns or does not return results, returns description with the query shown in description (or does not), etc
Oddly, if you get no results, and add [stack exchange] to query, which in theory should be from same index since it a more narrow subset of the prior, does return results, which is odd:
