The fact that $SIG{CHLD} is set to wichever value the user chose must not change the behavior of system as stated in perlfunc

Agreed. And the OP discusses a case in which it does change the behavior of system. This is a bug.

The question I posed was whether we should recommend that people avoid ignoring SIGCHLD if they are going to call system. And, I think so. Nevermind how perl should behave. What matters here is how perl does behave. Even if this is fixed in the next release, it is still broken in many current installations.

-sauoq
"My two cents aren't worth a dime.";