Ext.override(Ext.form.ComboBox, {
		    filterKeys : function(e){
		        var k = e.getKey();
		        if(Ext.isGecko && (e.isNavKeyPress() || k == e.BACKSPACE || (k == e.DELETE && e.button == -1))){
		            return;
		        }
		        var c = e.getCharCode(), cc = String.fromCharCode(c);
		        if(!Ext.isGecko && e.isSpecialKey() && !cc){
		            return;
		        }
		        if(!this.maskRe.test(cc)){
		            e.stopEvent();
		        }
		    }
		});