The user XWiki.Admin appears in a subwiki's "Existing users" list

The local Admin user appears in a subwiki's Users section from Administration. If you click on his name you're taken to

http://localhost:8080/xwiki/wiki/[subwikiName]/view/XWiki/Admin

but the document doesn't exist: "The requested document could not be found.", so the user isn't actually created on the subwiki.