I ran into the same problem where I couldn't get a Button click event to fire off until I did what CConchelos tried:
"2. I have fixed my postback issues by adding a hidden field to each accordion pane at page_init. I don't know why this fixes the erradic behavior, but it does."
Here's a basic example:
<body>
<form id="form1" runat="server">
<asp:ScriptManager ID="ScriptManager1" runat="server" />
<div>
</div>
<cc1:Accordion ID="Accordion1" runat="server">
<Panes>
<cc1:AccordionPane ID="AccordionPane1" runat="server">
<Header>Test1</Header>
<Content>
<asp:LinkButton ID="LinkButton1" runat="server">LinkButton</asp:LinkButton>
</Content>
</cc1:AccordionPane>
<cc1:AccordionPane ID="AccordionPane2" runat="server">
<Header>Test2</Header>
<Content>
<asp:Button ID="Button1" runat="server" Text="Button" />
</Content>
</cc1:AccordionPane>
</Panes>
</cc1:Accordion>
</form>
</body>
The Button1 click event would not get called until I added a hidden field to the AccordionPane that contained Button1 on the Page_Init:
Private Sub Page_Init(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Init
Dim myAccordionPane As AccordionPane
Dim myTextBox As New TextBox
myTextBox.Visible = False
myAccordionPane = MyBase.FindControl("AccordionPane2")
myAccordionPane.Controls.Add(myTextBox)
End Sub
I think Astynax777 is right - there must be something wrong with the controls inside an AccordionPane when being rendered.