The content management system will interpret any number at the end of a link as an Id for an article in the system. So, if you're trying to create a redirect from a url such as this...
...the system will interpret that 2013 number as an article id and attempt to match it. If an article with id 2013 exists, it will display that article. If it doesn't, it will display a 404 Page Not Found error.
To remedy this situation, we'd recommend that you modify the end of your redirect to include alpha characters ahead of the number:
This will allow the redirect to properly send the visitor to the destination url.
If this isn't feasible given your circumstance, feel free to submit a ticket.