@PaulW2U,
Please let me be clear,
This happened in Gome-Shell with Adwaita, too?
Anyway this might be caused new ubuntu specific patch what unveiled from 3.18.5-1ubuntu1 package:
Code:
diff --git a/gtk/gtkwindow.c b/gtk/gtkwindow.c
index 2d9f4b5..0476b6b 100644
--- a/gtk/gtkwindow.c
+++ b/gtk/gtkwindow.c
@@ -7122,6 +7122,11 @@ gtk_window_realize (GtkWidget *widget)
gtk_widget_register_window (widget, gdk_window);
gtk_widget_set_realized (widget, TRUE);
+ G_GNUC_BEGIN_IGNORE_DEPRECATIONS
+ if (!gtk_widget_get_app_paintable (widget))
+ gtk_style_context_set_background (gtk_widget_get_style_context (widget), gdk_window);
+ G_GNUC_END_IGNORE_DEPRECATIONS
+
attributes.x = allocation.x;
attributes.y = allocation.y;
attributes.width = allocation.width;
--
2.6.2
This patch seems very dangerous... 
I'm now building Gtk+ 3.19.2 with the patch and soon I'm going to test it on metacity 3.18.1.
And that patch could solve black flickering on opening windows on Compiz really?
Regards.
Tista
EDIT #1
OK. I could confirm that patch broke Mutter's window decorations by drawing solid background in shadow areas...
This patch (0001-gtkwindow-continue-calling-gtk_style_context_set_bac.patch) should be removed ASAP since the downside effects was too heavy and critical.
I can not understand why the contributors did not review this patch on Mutter...
EDIT #2
It affects to Metacity's window decorations, too.
Seems the worst patchworks in Gtk+ ever...
