As this one appeared to be odd:
Broken packages in rpmfusion-free-updates-testing-12-x86_64:
ffmpegthumbnailer-devel-2.0.1-1.fc12.i686 requires libffmpegthumbnailer.so.4
xtables-addons-devel-1.25-1.fc12.i686 requires libxt_ACCOUNT_cl.so.0
Multilib compose didn't pull in the dependencies here.
Just checked several other i686 -devel packages in the x86_64 repo, and it
has stopped working weeks ago. The F12 release repo is not affected.
Configuration issue?