Your package lxpanel failed to build from source in current rawhide. http://koji.fedoraproject.org/koji/taskinfo?taskID=6951498 For details on mass rebuild see https://fedoraproject.org/wiki/Fedora_21_Mass_Rebuild
Created attachment 904006 [details] build.log
Created attachment 904007 [details] root.log
Created attachment 904008 [details] state.log
Cause is bug 1037185 (-Werror=format-security).