I noticed that when I enable this gadget
https://test.wikipedia.org/wiki/Special:Gadgets/export/EditTools
and go to
https://test.wikipedia.org/w/index.php?title=TestPage&action=edit&debug=1
the HTML source code of the page contains two copies of
https://test.wikipedia.org/w/index.php?title=MediaWiki:Gadget-EditTools.css&oldid=144099
Indeed, searching for elements containing "ext.gadget.EditTools& on Google Chrome 21.0.1180.89 I find:
<link rel="stylesheet" href="//test.wikipedia.org/w/load.php?debug=true&lang=en&modules=ext.gadget.EditTools&>>
and
<link type="text/css" rel="stylesheet" href="//test.wikipedia.org/w/load.php?debug=true&lang=en&modules=ext.gadget.EditTools&>>
The same happens for "ext.gadget.hlist-test&>
<link rel="stylesheet" href="//test.wikipedia.org/w/load.php?debug=true&lang=en&modules=ext.gadget.hlist-test&>> <link type="text/css" rel="stylesheet" href="//test.wikipedia.org/w/load.php?debug=true&lang=en&modules=ext.gadget.hlist-test&>>