arraylist not binding to listbox

In my application, I am adding store items from UI to the arraylist and then binding the arraylist to listbox. But when i tried to add one more item it is getting updated there itself .It is not creating in new row. why is that so?

 my code is ,

store s1 = new store();

s1.itemname = txtIname.text;

s1.itemdesc = txtdesc.text ;

s1.ISBN = txtisbn.text;

I have a class named "mainstore"  that has arraylist method called (StoreInfo)  holding all these item details .

mainstore m = new mainstore();

m.insertstoreitems(s1);

it goes to  mainstore class and calls the method StoreInfo method that is of type arraylist.

it is successfully getting inserted into my arraylist.

 but back to UI

lbdisplay.DataSource = m.StoreInfo;

lb ...