Last modified: 2013-01-03 14:27:10 UTC
Under the user settings where is an option to preview an user skin. By modifying the URL you can also use that function on other pages than the main page, for example: https://en.wikipedia.org/w/index.php?title=user:Jimbo&useskin=standard This could be used to spread URLs with a modified wiki-interface and should be fixed.
This is not a bug. &useskin working on any page is an intentional feature.