Last modified: 2014-07-15 19:00:42 UTC
The code at https://github.com/wikimedia/mediawiki-core/blob/7313978c1959c716d6a1224b3ec8f4b7ead8134e/includes/Title.php#L3522-L3527 checks if $this->isJsSubpage() or $this->isCssSubpage(), but it doesn't seems to consider JS and CSS in the MediaWiki namespace.
Yep!
Moving to Page editing; the ContentHandler are fine in this regard (they identify the script, we're just not using it).