Add AjaxControlToolkit accordion pane at runtime loses previous pane(s)

Question

I have an AjaxControlToolkit accordion control that i'm trying to load panes at runtime. When I click a button inside a listview, it should add a new pane to the accordion control. Here is the code that adds the pane in the onitemcommand event within the listview

var pane = new AccordionPane { ID = key };
pane.HeaderContainer.Controls.Add(new LiteralControl(label.Text));
pane.ContentContainer.Controls.Add(LoadControl("~/UserControls/Covers/" + e.CommandArgument + ".ascx"));
accordion.Panes.Add(pane);

And this will successfully show a webcontrol inside the accordion control. But when I click on another button in the listview, the accordion is reset and it only shows the new pane instead of appending a new pane.

Is there any way to keep the previous pane visible across postbacks like this? By the way, each of the webcontrols that are loaded in the accordion have input fields that will need to be persisted across postbacks as well.

thanks!