According to http://linux.derkeiler.com/Mailing-Lists/Fedora/2005-07/1175.html this is a known bug that was fixed in 2.6.11, however, I'm running 2.6.18 (as updated with `yum update`)
It could be something new. I got dst cache overflows before and it was a while before they finally identified the bug for the one I saw. Some references below. All I remember was that the chap who finally paid some attention really had to dig through the code before he found it and informed Dave Miller.
http://oss.sgi.com/cgi-bin/extract-mesg.cgi?a=netdev&m=2004-06&i=40C...