I'm using Mediawiki 1.12.0. In LocalSettings.php, I set $wgCheckFileExtensions to false and I didn't update $wgFileExtensions (using default parameters).
However, even with $wgCheckFileExtensions set to false, I'm not able to upload a PDF file (for example). Of course, if I add 'pdf' on $wgFileExtensions array, it works as expected.
What I would expect : when $wgCheckFileExtensions is set to false, no extension checking should take place.
This bug is also described in the manual page (http://www.mediawiki.org/wiki/Manual:%24wgCheckFileExtensions) but doesn't seem to be filed in Bugzilla.
MediaWiki 1.12.0 (r32735) PHP 5.2.6-pl1-gentoo (apache2handler) MySQL 5.0.54