Transcient error in Koji/F15 (mock)

[Patrick Monnerat]

While packaging a new version of xca, the initial "fedpkg build" for F15
failed with error "BuildrootError: could not init mock buildroot, mock
exited with status 4; see root.log for more information". See
http://koji.fedoraproject.org/koji/taskinfo?taskID=4059840

I thus examined all the log files and could not find a real error.
Resubmitting exactly the same build 50min later succeeded:
http://koji.fedoraproject.org/koji/taskinfo?taskID=4059927

I don't know where the failure comes from: koji? mock? infrastructure?
Where to submit a bug report for it?

Thanks for hints/dispatching.

Cheers,
Patrick