popen() in multithreaded program - hangs?

I'm trying to write a client for the jack audio connection kit
(http://jackaudio.org), have hit an apparent bug and am not sure
who's at fault.
 
This is the client:
 
--
 
#include <jack/jack.h>
#include <err.h>
 
jack_port_t *input_port;
jack_port_t *output_port;
jack_client_t *client;
 
int
main (void)
{
  jack_status_t status;
 
  client = jack_client_open ("cdemo", JackNoStartServer, &status, "default");
  if (!client) errx (112, "client_open: could not");
 
  jack_client_close (client);
  return 0;
}
 
--
 
The jack_client_open() call never returns and the process can only be killed
with SIGKILL. Tracing execution in gdb shows that the hang occurs in the
popen() call in jack_get_tmpdir(), defined at client.c:114:
 
  http://trac.jackaudio.org/browser/trunk/jack/libjack/client.c
 
Is there a known issue with calling popen() in a multithreaded program? At
the point of that call, on my system, there are three running threads.
 
Any help/advice on how to resolve this problem would be appreciated.
 
xw