LWW4.3.7 call-system and friends leaking handles

I am running into problems using call-system-showing-output to run a
large number of external commands.  

It appears that each call is leaking up to 4 handles - named pipes and
processes.  Eventually my entire system hits the buffers as windows runs
out of handles.

open-pipe exhibits the same problem.

You can see this behaviour nicely using process explorer from
http://www.sysinternals.com/ntw2k/freeware/procexp.shtml

Is there any way around this other than closing down the app to release
the handles (which is not really an option) ?

- Dominic