normalize IE8 input checked setter

Source/Element/Element.Event.js

@@ -171,14 +171,33 @@ if ('onmouseenter' in document.documentElement){
 }
 
 /*<ltIE9>*/
+var inputClickWatcher = false;
+function isBuggyType(e){
+	return e.type == 'propertychange' && e.event.propertyName == 'checked';
+}
+function isSyntetic(){
+	var clicked = inputClickWatcher;
+	inputClickWatcher = false; // reset the flag
+	return clicked ? false : true;
+}
 if (!window.addEventListener){
 	Element.NativeEvents.propertychange = 2;
 	Element.Events.change = {
 		base: function(){
 			var type = this.type;
 			return (this.get('tag') == 'input' && (type == 'radio' || type == 'checkbox')) ? 'propertychange' : 'change';
 		},
+		onAdd: function(event){
+			this.addEvent('click', function(event){
+				inputClickWatcher = true;
+				event.stop();
+			});
+		},
 		condition: function(event){
+			if (isBuggyType(event) && isSyntetic(event)) return false;
+			var el = event.target;
+			if (el.type == 'checkbox') el.checked = !el.checked;
+			if (el.type == 'radio' && !el.checked) el.checked = !el.checked;
 			return event.type != 'propertychange' || event.event.propertyName == 'checked';
 		}
 	};

Specs/Element/Element.Event.js

@@ -334,6 +334,34 @@ describe('Element.Event.change', function(){
 
 });
 
+describe('Element.Event.change', function(){
+    /*<ltIE9>*/
+
+    var checked, eventFired;
+    var input = new Element('input', {
+        type: 'checkbox'
+    });
+    input.addEvent('change', function(e){
+        eventFired = true;
+    }).inject(document.body);
+    it('should not fire any event when setting a "checked" property', function(){
+        input.set('checked', true);
+        checked = input.get('checked');
+
+        expect(checked).toBeTruthy();
+        expect(eventFired).not.toBeTruthy();
+    });
+
+    it('should fire a change event when clicking a input[type=checkbox]', function(){
+        input.click();
+        checked = input.get('checked');
+
+        expect(checked).not.toBeTruthy();
+        expect(eventFired).toBeTruthy();
+    });
+});
+ /*</ltIE9>*/
+
 describe('Element.Event keyup with f<key>', function(){
 
 	it('should pass event.key == f2 when pressing f2 on keyup and keydown', function(){