This is a bandaid which fixes anoyance in dialogs which appear when creating
variable widgets like HBox.

The sppin editor is used in multiple places but only htese dialogs have a
default button so it is safe to set the spinbutton to activate default
unconditionally. Does not seem to break anything.

diff -ur glade-3-3.8.0/gladeui/glade-editor-property.c glade-3-3.8.0.mod/gladeui/glade-editor-property.c
--- glade-3-3.8.0/gladeui/glade-editor-property.c	2011-08-26 16:50:09.000000000 +0200
+++ glade-3-3.8.0.mod/gladeui/glade-editor-property.c	2011-08-26 16:40:12.000000000 +0200
@@ -746,6 +746,7 @@
 						   G_IS_PARAM_SPEC_FLOAT (eprop->klass->pspec) ||
 						   G_IS_PARAM_SPEC_DOUBLE (eprop->klass->pspec)
 						   ? 2 : 0);
+	gtk_entry_set_activates_default (GTK_ENTRY(eprop_numeric->spin), TRUE);
 	gtk_widget_show (eprop_numeric->spin);
 	
 	g_signal_connect (G_OBJECT (eprop_numeric->spin), "value_changed",
