With the tree in flux as it is I keep getting failed updates caused by packages that are not found. In this situation up2date reports a 404 error and aborts. It should be checking the other mirrors or offering to do so.
Also, this is needed in order for up2date to be able to deal with a mirror not having a specific ARCH - see also bug 116860.
*** Bug 118410 has been marked as a duplicate of this bug. ***
Obsolete bug - yum has replaced up2crate