[Zope] popen2, popen3, popen4 and Zope

The popen libraries don't seem to function properly when used from a Zope External Method or product. I use the standard idiom -- i, o = os.popen2( cmd ) i.close() res = o.read() but Zope seems to hangs on the read whenever cmd is anything of any complexity, for example, a shell script that fires off a python instance that detaches itself and then initiates another insance of Zope. Is the problem a threading issue? Is there a preferred mechanism for spawning a process?