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As per @pmario's comment at 582b156d5f (commitcomment-51566608)

core/modules/widgets/widget.js

@@ -569,8 +569,9 @@ Widget.prototype.invokeActions = function(triggeringWidget,event) {
 	// For each child widget
 	for(var t=0; t<this.children.length; t++) {
 		var child = this.children[t];
-		// Invoke the child if it is an action widget
+		// Rerender the child to ensure the attribute values are up to date
 		child.refreshSelf();
+		// Invoke the child if it is an action widget
 		if(child.invokeAction) {
 			if(child.invokeAction(triggeringWidget,event)) {
 				handled = true;