Trouble with button mask

[James Steward <jamessteward optusnet com au>]

Hi,

I've been trying to get a canvas select item event to fire for a 
gtk_plot_canvas.

Upon left clicking inside a plot canvas, I can see that 
gtk_plot_canvas_button_press(...) gets called, and the following lines 
near the beginning of that function (in the gtkextra lib) cause the 
function to exit without anything being selected.

  gdk_window_get_pointer(widget->window, NULL, NULL, &mods);
  if(!(mods & GDK_BUTTON1_MASK)) return FALSE;

Upon inspection of the variable "mods", it appears to have a value of 
GDK_MOD2_MASK, according to GDB.

Anyone know why a GDK_BUTTON1_MASK isn't read when I left click?

Regards,
James.