Running Expect 5.38.2 under Solaris 2.6.  Most of the time there is no problem, but occasionally, Expect will seem to hang.

Running an in-house application called "netpoll" which spawns FTP.  When the hang occurs, I see three processes (parent, child, grandchild) instead of two:

      <user> 17570 17568   TS  18   Mar 12 pts/57   0:00 expect -- netpoll <params>
     <user> 17531     1   TS  58   Mar 12 ?        0:00 expect -- netpoll <params>
     <user> 17568 17531   TS  18   Mar 12 pts/57   0:00 expect -- netpoll <params>

# truss -p 17531
read(17, 0xEFFFE77B, 1)         (sleeping...)
# truss -p 17568
vfork()         (waiting for child to exit()/exec()...)
truss -p 17570
lwp_mutex_lock(0xEF7ED0D8)      (sleeping...)