Weird problem building zsh in local mock but not in koji

[Jason L Tibbitts III]

I'm having a problem building the current zsh srpm
(zsh-4.3.10-4.fc13.src.rpm) on my local builder, which runs F11-x86_64
and has mock-0.9.18-1.fc11.noarch.  On IRC, a user reported the same
problem, only his builder runs CentOS 5.4 and has
mock-0.9.14-2.el5.noarch.  Surprisingly, the same srpm will build fine
in koji.

I'm not sure how to describe the hang in enough detail without having to
understand the zsh test framework.  The bottom line is simply that one
of the tests just hangs.  It's doing some testing of the read builtin; I
believe it's one of these two stanzas which hangs, although output
buffering may make it difficult to be sure:

 read -d: <<<foo:bar
 print $REPLY
0:read up to delimiter
> foo 
 print foo:bar|IFS=: read -A
 print $reply
0:use different, IFS separator to array
> foo bar 
The last thing in the build log is "Running test: read up to delimiter".
ps just shows:

tibbs       9322  0.0  0.0 114684  1916 pts/3    TN   12:39 00:00:00  ../Src/zsh +Z -f
./ztst.zsh ./B04read.ztst

wchan is signal_stop.  The process doesn't seem to be consuming any CPU,
but if I strace it, I get an endless stream of

ioctl(11, SNDCTL_TMR_STOP or TCSETSW, {B38400 opost isig -icanon echo...}) = ? ERESTARTSYS
(To be restarted)
--- SIGTTOU (Stopped (tty output)) @ 0 (0) ---
--- SIGTTOU (Stopped (tty output)) @ 0 (0) ---


In koji there doesn't seem to be any delay at all running this test.
I'm stumped.

 - J<