[gtkmm] Problem with Glib::signal_io

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I'm trying to use a caracter device that uses the parallel port for the 
comunication.
I create a driver for this device, which works well (I used it in another 
proyect with another graphic library).


Here is the code:

paralelo.hh
***********

#ifndef _PARALELO_HH
#define _PARALELO_HH

#include "config.h"
#include <iostream>
#include <stdio.h>
#include <sys/shm.h>
#include <glib-2.0/glib.h>
#include <unistd.h>

#include <gtkmm.h>
#include <sigc++/signal.h>

#include <sys/ioctl.h>

class paralelo : public SigC::Object
{
public:

 paralelo();
 virtual ~paralelo();

 gchar port[50];
 gint fd;

 gint start();

 bool callback_funcion(Glib::IOCondition);

protected:

private:


 SigC::Connection conexion;

};
#endif


paralelo.cc
*************

#include "paralelo.hh"

// Start the listening
gint paralelo::start()
{

 this->fd = open(this->port, O_RDWR);

 if(this->fd<0)
 {
   // ERROR
 }


 this->conexion = 
Glib::signal_io().connect(SigC::slot(*this,&paralelo::callback_funcion),
                                            this->fd,
					     //Glib::IOChannel::create_from_fd(this->fd), // I've also try 
this, but the same result
					     Glib::IO_IN);

 return 0;
}


The problem is that when the start function is called, the callback_funcion 
is executed all the time, behaving as the device has always something to 
read.
The same code with a normal serial port works well (the callback_funcion is 
only called when there is something on the port, not all the time).

The driver worked well on a RedHat 7.1 with a kernel 2.4.18-1 and Xforms 
graphic library (yes this graphic library is quite old :-) ).
Actually I'm using RedHat 8.0, with a kernel 2.4.18-14, gtkmm-2.0 and 
sigc++-1.2.

The driver for the device doesn't implement all the function of a caracter 
device (for example the flush option is disabled), and some other don't 
behave as a caracter device should do (for example the read function works 
diferent).
Could this affect the behaviour of the signal_io function???

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