strangeness of g_signal_connect

[Colossus <colossus 3000 it>]

Hi,

In my app I have the following:

g_signal_connect ((gpointer) AddFile_button, "clicked",
                    G_CALLBACK (on_add_files_activate),
                    "dummy");

I have noticed that if the function "on_add_files_activate" is 
declared with only one parameter, gpointer data , I never receive the 
word dummy. Instead if  the same function is declared with two parameters:

void on_add_files_activate ( GtkWidget *useless , gpointer data);
I can successfull print the value "dummy" pointed by data.

Could gtk developers explain this strange behaviour please ?
--
Colossus

Cpsed, a Linux OpenGL 3D scene editor
http://cpsed.sourceforge.net/