Self-trackbacks misreading permalinks and pinging wrong entry

For some reason when I do a self-ping, it pings the entry for the year of the post I intended to ping. For example, my permalink structure is:

http://www.mydomain.com/index.php/2005/01/22/post-name

If I were to write an entry that referenced the above, the ping would show up on post ID #2005. It’s been doing this for a little while – probably since I upgraded to 2.0 – but I only just noticed it because I’ve been self-pinging entries from 2005 and I only just now pinged an entry from 2002 – and that ended up landing on post ID #2002.

Any idea what gives?