This is copied over from Joomlacode, since the bug is still present. http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_id=8103&tracker_item_id=31557

How to reproduce the problem and/or test the patch:: Install Joomla, enable mod_rewrite SEF, have the homepage be a featured view from com_content, look up a random article id in the backend, type the URL

http://domain.tld/-blarg

You don't get a 404 and instead a valid site with the homepage itemid and the article with the article id.

When Joomla receives a request with a non-existant URL, it should properly throw a 404 error. Right now, this is not the case.
If you call Joomla with an invalid URL that starts with a number followed by a dash and then some giberish and the number corresponds to an existing article, you get a 200 response with the article with the ID that is corresponding to the number at the beginning of the URL. That site has the Itemid of the homepage.
This means that right now we have at least 3 different URLs for accessing an article with different Itemids.
This bug is present both in 2.5 and 3.1.
I actually don't really want to look through the router any further and find all the current bugs. If there is an interest, I would provide a rewrite of the router for the core components based on the routers from 1.6 for the 2.5 development line. That would also include the HelperRoute classes mentioned in the other bug reports. For 3.x, I'd still like to advocate a complete rewrite of the routing system.