Weird issue with pipeviewer and multiple pipes

[Jason L Tibbitts III <tibbs@math.uh.edu>]

Someone brought this up on IRC; I thought I'd bring it to a larger
audience.  

Pipeviewer (pv) is a little program that sits in a pipeline, passes data
through, and outputs some progress information.
  http://www.ivarch.com/programs/pv.shtml
I didn't know about it until today, but it's kind of neat.  It's in most
distros/repositories/package managers/whatever.

Run this:
  echo 1 | pv -l -s $(echo 1)

Should give '1' and a progress bar.  Now tack on "|cat".  For me that
hangs.  ctrl-Z does nothing.  ctrl-C seems to do what I'd expect ctrl-Z
to do:

[2]  + 11459 done                    echo 1 |
       11461 suspended (tty output)  pv -l -s $(echo 1) |
       11462 interrupt               cat

If I type fg, the shell is pretty much hung.  You have to kill -9 the pv
process either way to get rid of the job.  (Lesser kills don't seem to
work.)

Could certainly be a bug in pv, but it's definitely weird and I'd just
dismiss it except that other shells seem to have no problems.

 - J<