Repainting Cairo windows?

I am facing a problem that I suspect is to do draw / paint elements in cairo.

I have a borderless window in pygtk but I am drawing two rectangles with cairo.a a black rectangle and a gray rectangle inside. When the window is resized, it appears that parts of the inner rectangle are not being drawn / painted. I have included 3 screenshots to show this problem.

As you can see in the second and third pictures, some parts of the window are not grayed out. One way to fix this is to call the pygtk window present () method, but this makes my program quite slow as the window height changes with almost every key press. So I was wondering what alternatives I need to fix.

below is the corresponding cairo code i am using

def expose(self, widget, e):
    cr = widget.window.cairo_create()

    # Draw the background
    cr.set_operator(cairo.OPERATOR_SOURCE)

    # Create black rectangle with 60% opacity (serves as border)
    (width, height) = widget.get_size()
    cr.set_source_rgba(0, 0, 0, 0.6)
    cr.rectangle(0, 0, width, height)
    cr.fill()

    # Inside the black rectangle, put a lighter one (will hold widgets)
    (width, height) = widget.get_size()
    cr.set_source_rgb(205/255, 205/255, 193/255)
    cr.rectangle(10, 10, width-20, height-20)
    cr.fill()   

    return False

def screen_changed(self, widget, old_screen = None):
    screen = widget.get_screen()
    colormap = screen.get_rgba_colormap()
    widget.set_colormap(colormap)