Adding another select option to button

Hello, I'm having really hard time in adding another select option into default button code. What i want to do is to add class to button depending on selected value from select box (small,medium,big). 

Everything works ok for first button, after i add another one i have class on that but class from first one is removed. Also if i add 4 buttons in one save they have right classes if i add another one after that only last has class.

I'm using wordpress backend for this feature and here is my code from button.js

contents : [{
			id : "info",
			label : b.lang.forms.button.title,
			title : b.lang.forms.button.title,
			elements : [{
				id : "name",
				type : "text",
				label : b.lang.common.name,
				"default" : "",
				setup : function(a) {
					this.setValue(a.data("cke-saved-name") || a.getAttribute("name") || "")
				},
				commit : d
			}, {
				id : "value",
				type : "text",
				label : b.lang.forms.button.text,
				accessKey : "V",
				"default" : "",
				setup : function(a) {
					this.setValue(a.getAttribute("value") || "")
				},
				commit : d
			}, {
				id : "type",
				type : "select",
				label : b.lang.forms.button.type,
				"default" : "button",
				accessKey : "T",
				items : [[b.lang.forms.button.typeBtn, "button"], [b.lang.forms.button.typeSbm, "submit"], [b.lang.forms.button.typeRst, "reset"]],
				setup : function(a) {
					this.setValue(a.getAttribute("type") || "")
				},
				commit : d
			},{
				id : "class",
				type : "select",
				label : b.lang.forms.button.cla,
				"default" : "button-small",
				accessKey : "T",
				items : [[b.lang.forms.button.classS, "button-small"], [b.lang.forms.button.classM, "button-medium"], [b.lang.forms.button.classB, "button-big"]],
				setup : function(a) {
					this.setValue(a.getAttribute("class") || "")
				},
				commit : d
			}]