The following piece of code examines the problem a bit further, along the guidelines of perlport:

#!/usr/bin/perl
use POSIX;
if(@ARGV){ $SIG{'CHLD'} = 'IGNORE'; }
system('./prog2.pl');
$status=$?;

if(WIFEXITED($status)){
 print "prog2.pl exited normally, returning ",
       WEXITSTATUS($status), "\n";
}elsif(WIFSIGNALED($status)){
 print "prog2.pl was terminated with signal ",
       WTERMSIG($status), "\n";
}elsif(WIFSTOPPED($status)){
 print "prog2.pl is stopped for signal ",
       WSTOPSIG($status), "\n";
}else{
 print "can't understand what happened to prog2.pl; ",
       "status is ",$status,"\n";
}
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When I ran it under perl 5.8.0 (on i386 linux, kernel 2.4.20, glibc 2.3.2), I got the following results:

#./prog1.pl
prog2.pl exited normally, returning 5
#./prog1.pl ignore
prog2.pl was terminated with signal 127

Interesting enough, no POSIX signal has number 127, AFAIK... something is not working here.
Ant9000