System V behaviour is broken because it violates the least surprise
principle and adds an exception. More, it is not logical. Default
behaviour for SIGCHLD is to not kill the process and to not call any
routine, in other words, "ignore". Setting a signal handler to SIG_IGN
while it is yet ignored should cause to get the child to be "more
ignored than ignored"? Ouch.
It may very well be broken, but it may be one of the things that we have
to grit our teeth and accept if we want Unix branding, since I wouldn't
be surprised if this sort of thing is in Spec 1170.
- Ted