rpm-4.2.1-0.29 psm reaper isn't reaping the child processes from the %pre/%post scripts, so everything grinds to a halt and the child process stays on as a zombie. This is an old bug that either never got fixed or just returned.
My latest understanding of this bug: - rpm 4.3 has the fix, a rewrite of the package state machine - The fix was deemed (by someone besides jbj) as too intrusive to go into rpm 4.2.x