In the following snippet the list's items are added after the list is 
shown (they're added at "position 2"), so no item is initially selected.  
The problem is that selecting a list item then causes 2 selection events 
to fire instead of the expected 1 selection event.

Moving the item-creation lines from "position 2" to "position 1" makes the 
problem go away, presumably because the first item is initially selected 
for free.

#include <gtk/gtk.h>
void changed (int a, int b) {
  g_print("selection\n");
}
int main (int argc, char *argv[]) {
  GtkWidget *window, *sw, *box;
  GtkTreeViewColumn *column;
  GtkTreeIter iter1, iter2;
  GtkListStore *store;
  GtkWidget *tree;
  GtkCellRenderer *renderer;
  GtkTreeSelection *selection;

  gtk_init (&argc, &argv);
  window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
  gtk_window_set_default_size (GTK_WINDOW (window), 200, 200);
  box = gtk_hbox_new (FALSE, 0);
  gtk_container_add (GTK_CONTAINER(window), box);
  sw = gtk_scrolled_window_new (NULL, NULL);
  store = gtk_list_store_new (1, G_TYPE_STRING);
  tree = gtk_tree_view_new_with_model (GTK_TREE_MODEL (store));
  g_object_unref (G_OBJECT (store));
  renderer = gtk_cell_renderer_text_new ();
  column = gtk_tree_view_column_new_with_attributes (
    0, renderer, "text", 0, NULL);
  gtk_tree_view_append_column (GTK_TREE_VIEW (tree), column);
  selection = gtk_tree_view_get_selection(GTK_TREE_VIEW (tree));
  gtk_tree_selection_set_mode (selection, GTK_SELECTION_BROWSE);
  g_signal_connect (selection, "changed", G_CALLBACK(changed), NULL);
  gtk_box_pack_start (GTK_BOX(box), sw, TRUE, TRUE, 0);
  gtk_container_add ((GtkContainer *)sw, tree);

  /* position 1 */

  gtk_widget_show_all(window);

  /* position 2 */
  gtk_list_store_append (store, &iter1);
  gtk_list_store_set (store, &iter1, 0, "item 1", -1);
  gtk_list_store_append (store, &iter2);
  gtk_list_store_set (store, &iter2, 0, "item 2", -1);

  gtk_main();
  return 0;
}