Comment # 2 on bug 898723 from Archie Cobbs

I think this problem occurred after I accidentally ran two separate createrepo
processes simultaneously on the same repository. Obviously that was my mistake,
however it does reveal a bug in some uncommonly used part of the code.

This may or may not be worth investigating. I figured since it has a stack
trace it may be easy to debug. If not, try running two createrepo's at the same
time, letting one or both crash, and then running a single createrepo against
the partially created repo.