The fact that it's a special page error is a separate bug (we need to implement a real Badtitle special page).

The bug appears to be due to our title handling:

http://svn.wikimedia.org/viewvc/mediawiki/trunk/phase3/includes/Wiki.php?view=markup#l62

Instead of calling Title::newFromURL the code that handles the &curid= activates when you have a &curid= however because the title was deleted and the page_id no longer exists Title::newFromID returns null and Badtitle is returned.

I think we should change that set of code to work on the "if it's not set model". ie: Instead of elseif, each of those blocks is a if ( is_null( $ret ) && [...] ) then if any case is active but the Title:: for that case returns null the next case will activate.

In the case of a &curid=###&title= if &curid= exists it will override but if it doesn't &title= will return a title.

EXAMPLE: http://en.wikipedia.org/w/index.php?curid=1

http://en.wikipedia.org/w/index.php?title=Foo|Bar&action=history

tagging bugs for Marcus to look at

Another example (namespace with empty page part) - http://en.wikipedia.org/wiki/User:

(In reply to comment #5)

Another example (namespace with empty page part) -
http://en.wikipedia.org/wiki/User:

That's a little more to do with us not having a proper Badtitle page, than with the other oldid bug.