Michael.Keppler wrote:

The testcase can be simplified to searching for "" (including the quotes),
probably because the English wikipedia uses 'the' as stopword.

As I can't reproduce the exact behaviour on my test machine, I can only guess
that the problem is in line 126 of SpecialPage.php, which is
...
if( '' === trim( $term ) ) {
...

But in case of quoted search strings this condition is not fulfilled (although
it should be, cause this condition is responsible for the "bad query" output).
Maybe someone can confirm this assumption?

BTW: An interesting thing is that there is an article "the the", which is found
if you use the "Go" button of the search field in the quickbar with the term
"the the" (including quotes), but not using "Search" (where you get the results
described in this bug). Maybe someone could have a look at that phenomenon too...

richholton wrote:

I should note that this did work for a while under the new Lucene search engine.
I can't say exactly when it stopped working, but I think it was sometime in the
past week.

zigger wrote:

This example is currently working again.

See also bug 2222 where the search term AND also gets a "search disabled"
result, depending on companion terms.