yes, :0cw works

Well, I tried it out, and my suggestion for Jesper Pedersen's question
to launch the clone with

 :0cw
 {

does work.  The parent procmail will wait until the clone has exited -- and
if the clone falls through its original braces (intentionally or otherwise)
and reads later code in the rcfile, the parent will keep on waiting until
the clone finishes completely.

That way the parent will not write to the logfile while the clone is active,
and messages from the two will not be interleaved.

DWT