I'm not sure this is the correct place to post this, but I've found some glaring bugs in both the TabContainer and Accordion controls.
I did not notice this before until I decided to put more than 1 DropDownList in a TabContainer with AutoPostBack="true"

Create a form, add a TabContainer and add a TabPanel.
Inside the TabPanel, add 3 dropdownLists (w/some dummy data) in the ContentTemplate
Set AutoPostBack="true" on the controls.
On the code behind, create 3 event handlers for the SelectedIndexChanged events.
Put a break point on each of the 3 subs.

Run the page.

Make a selection from 1 of the dropDownLists:
The codebehind breakpoint for that DropDownList fires once, the first time it loads.
Now, step through the debugger til the page is refreshed again.
Now, go to a different dropDownList and make a selection.
- the page posts back a second time, but now, not only does the DropDownList you just changed SelectedIndexChanged event fire, but the PREVIOUS one you selected ALSO fires!
- Now change the selection of the 3rd DropDownList, and you will find that the other 2 DropDownLists will fire their SelectedIndexChanged events (even though they are not selected!).

The Accordion control has the same (extra event firing) problem.

<ajaxToolkit:TabContainer ID="tc1" runat="server" ActiveTabIndex="0" CssClass="TabStyles" Width="560px" EnableViewState="False">
        <ajaxToolkit:TabPanel ID="tp1" runat="server">
            <HeaderTemplate>tab 1</HeaderTemplate>
            <ContentTemplate>
                <asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="True">
                    <asp:ListItem>1</asp:ListItem>
                    <asp:ListItem>2</asp:ListItem>
                    <asp:ListItem>3</asp:ListItem>
                </asp:DropDownList>
                <asp:DropDownList ID="DropDownList2" runat="server" AutoPostBack="True">
                    <asp:ListItem>A</asp:ListItem>
                    <asp:ListItem>B</asp:ListItem>
                    <asp:ListItem>C</asp:ListItem>
                </asp:DropDownList>
                <asp:DropDownList ID="DropDownList3" runat="server" AutoPostBack="True">
                    <asp:ListItem>alpha</asp:ListItem>
                    <asp:ListItem>beta</asp:ListItem>
                    <asp:ListItem>gamma</asp:ListItem>
                </asp:DropDownList>
            </ContentTemplate>
        </ajaxToolkit:TabPanel>
    </ajaxToolkit:TabContainer>

    Protected Sub DropDownList1_SelectedIndexChanged(sender As Object, e As EventArgs) Handles DropDownList1.SelectedIndexChanged

    End Sub

    Protected Sub DropDownList2_SelectedIndexChanged(sender As Object, e As EventArgs) Handles DropDownList2.SelectedIndexChanged

    End Sub

    Protected Sub DropDownList3_SelectedIndexChanged(sender As Object, e As EventArgs) Handles DropDownList3.SelectedIndexChanged

    End Sub

I've spent 2 days trying different settings (ViewState on/off, using UpdatePanels, etc, etc.), but could not find any workaround for this.