There's some bug in site rendering that lets it mismatch tags
(<p><small></p></small>), which makes the page invalid XML, so it
can't be used to do AJAX-type things. This was making all edit pages
invalid XHTML on Commons because of a bug in the edittools box. See:
http://commons.wikimedia.org/wiki/MediaWiki_talk:Edittools#This_page_is_bre…
I thought the rendered HTML was passed through a validator/cleaner
program after rendering? Maybe this isn't used on things in the
Mediawiki: namespace?
There's also a bug that seems to involve over-correcting the markup
and adding an extra <p><br></p> sometimes. I've filed it as
http://bugzilla.wikimedia.org/show_bug.cgi?id=4843 Are these related
at all?