g_signal_connect seems not to work on Alpha

[Rob Clack <rnc sanger ac uk>]

I have an application which seems to work fine on a Compaq deskpro 
running Red Hat 9, but which is less fine on an HP Alpha running OSF1 
(not sure which version).

Specifically I have a foocanvas (stripped down gnome canvas, courtesy of 
Jodi Goldberg) on which I draw various canvas items which I then connect 
to my callback function like this:

      boundingBox = 		 
foo_canvas_item_new(FOO_CANVAS_GROUP(params->columnGroup),
                                        foo_canvas_rect_get_type(),
                                        "x1", (double)0.0,
                                        "y1", (double)5.0,
                                        "x2", (double)params->thisType->width,
                                        "y2", (double)params->height,
                                        "fill_color", "white",
                                        NULL);

      g_signal_connect(G_OBJECT(boundingBox), "event",
                       G_CALLBACK(handleCanvasEvent), params) ;

On the deskpro/Linux box, this works fine, but on the Alpha/OSF1 the 
event handler never gets called when I click on the canvas item.

I don't see anything in the archives that seems relevant to this, so I 
hope someone has seen this before and can point me in the right direction.

And if someone can point me at some documentation listing the events a 
canvas item responds to, that would be really handy, too.  Just having 
"event" is painful when debugging, but I can't find anything to tell me 
what else I can use.
Thanks
Rob Clack

The event handler function is here:

static gboolean handleCanvasEvent(GtkWidget *widget, GdkEventButton 
*event, gpointer data)
{
  ParamStruct *params = (ParamStruct*)data;
  ZMapFeatureContext feature_context;
  ZMapFeatureSet feature_set;
  ZMapFeature feature;
  const gchar *itemDataKey = "feature";
  FeatureKeys featureKeys;
  gboolean result = FALSE;  // if not a BUTTON_PRESS, leave for any 
other event handlers.

  if (event->type == GDK_BUTTON_PRESS)  // GDK_BUTTON_PRESS is 4
  {
    featureKeys = g_object_get_data(G_OBJECT(widget), itemDataKey);

    if (featureKeys && featureKeys->feature_key)
      {
	feature_set = 
g_datalist_id_get_data(&(params->feature_context->feature_sets), 
featureKeys->context_key);
	feature = g_datalist_id_get_data(&(feature_set->features), 
featureKeys->feature_key);
        featureClickCB(params, feature);
        result = TRUE;
      }
    if (event->button == 3)
      {
        itemDataKey = "feature_set";
        featureKeys = g_object_get_data(G_OBJECT(widget), itemDataKey);
        if (featureKeys)
          {
	    feature_set = 
g_datalist_id_get_data(&(params->feature_context->feature_sets), 
featureKeys->context_key);
            params->feature = feature;
            columnClickCB(params, feature_set);
            result = TRUE;
          }
      }
  }

  return result;
}