Hi,
I use Polylang with the Hide URL language indo for default language enabled. When I seach for empty string '' in the default language, I get results from both languages, not only the default language.
So for example http://example.com/?s=&submit=Search will return results from both languages, while http://example.com/?s=a&submit=Search recognizes that I am using the default language, so I get results from the default language only.
I think it's a bug.