I'm not sure whether this is relevant, but just in case… depending on your version of perl, it's at or near the end of the man page for fork:

Note that if your forked child inherits system file descriptors like STDIN and STDOUT that are actually connected by a pipe or socket, even if you exit, then the remote server (such as, say, a CGI script or a backgrounded job launched from a remote shell) won't think you're done. You should reopen those to /dev/null if it's any issue.