All my previous tests were from a fully upgraded 4.0 machine, and for those I had no trouble. With this one, a stock 4.0 machine with no upgrades, yum locked. Might be worth trying to reproduce it. Another interesting fact is that this was my only machine with SELinux active, but I'm still betting on a python/yum related problem.
And you'd lose that bet.
FUTEX lock happens between the kernel, rpm and bsddb.
go check out red hat bugzilla to look for the bugs reported on this problem.
-sv