I'm looking at IO::Socket::INET.pm, and it certainly does set $! under some circumstances, though it goes to great lengths to maintain $!, meaning that a previous value in $! can propogate through to snag the unwary.

Here's a simple way to duplicate the symptoms:

  use IO::Socket::INET;
  open(F, "<", "nosuchfile");  # set $!
  my $socket = new IO::Socket::INET();
  print "$!";  # prints "No such file or directory"
[download]