Note that the WYSIWYG editor currently generates an untyped link reference when the selected link type is url and the passed URL contains ://. See https://github.com/xwiki/xwiki-platform/blob/master/xwiki-platform-core/xwiki-platform-ckeditor/xwiki-platform-ckeditor-plugins/src/main/webjar/xwiki-link/plugin.js#L429-L432 . I don't remember the decision behind this though.
