I want to second on this. What is happening to the updates repository? This is crazy. If I want to do a rational yum update I have to keep disabling the updates repo.
I am also having this problem. I originally thought that it might be something to do with me installing some sort of 'tainted' package, but I've now experienced the problem on 4 separate machines running fc5 - two of which were new installs. I would also be interested in this getting fixed :-) Rob