Try checking to see what syswrite returns. Maybe your call is not writing all of buffer. If so syswrite will return how much it actually wrote. You could then used the offset parament of syswrite to continue to write the rest of the buffer. I have a similar app that writes data to a socket connection. Here is how I implement it... 
#
# Sub used to write data to FDMS.
# Writing requires that the first 6 bytes are NBxxxx
# where xxxx is the total number of bytes to write plus the NBxxxx.
#
sub write {
   my ($this, $buffer) = @_;
   my $thisSub = (caller(0))[3];
   my $socket = $this->{socket};
   my $select = $this->{select};
   my $verbose = $this->{verbose};
   my $timeout = $this->{writeTimeout};
   $buffer = sprintf('NB%04d%s', length($buffer) + 6, $buffer);
   my $length = length($buffer);
   my $offset;
   my $bytes;
   while ($length > 0) {
      if ($select->can_write($timeout)) {
         $bytes = $socket->syswrite($buffer, $length, $offset);
         croak "Unable to write: $!" unless defined $bytes;
         $offset += $bytes;
         $length -= $bytes;
         print "$thisSub($bytes) = $buffer\n" if $verbose;
      }
      else {
         croak 'timeout on write';
      }
   }
}

[download]

UPDATE:
try putting in a signal handler for SIGPIPE to see if you can get around the problem.
Something like... 
$SIG{PIPE} = sub { die "SIGPIPE\n"; };

[download]
...just to see if it is happening.

UPDATE:
See this post...
script dies with 'broken pipe'-message, even in eval

In reply to Re: Festival Module by mifflin
in thread Broken Pipe error when talking to Festival server by rsiedl

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