I found dozens of directories named 2.6.10-1.*_FC4smp in /lib/modules, even though I've never had any smp kernel installed on my rawhide-tracking box. That's because kernel-smp-devel caused the dir to be created because it owns the build and source subdirs, but since it doesn't own the parent dir, it never gets removed after an upgrade.
but the -devel rpm's *don't* own that dir. (The fact that it got created when it got installed is irrelevant here, typically, the parent is owned by the kernel-smp package itself). the problem here is why did that smp-devel package get installed in the first place when you had no smp kernel installed. I believe Jeremy fixed a bug in Anaconda a while ago that may have caused this.
No, the problem of having smp-devel packages installed was a separate bug. This one was about the fact that -devel installed files in a directory it didn't own, without a dep on the package that owned it, such than, in the absence of the dir owner, when the package was removed, the directory would be left behind. This has since been fixed by having the sources and build links in /lib/modules/`uname -r`/ moved to the kernel dirs, exchanging the need for dir (co-)owning for ugly dangling links when devel is not present. Yuck.