Request.Form cannot find dropdownlist on TabContainer.TabPanel

I call  InitializeCulture (override, see code from VB codebehind) as the result of a selectedIndex change from a dropdownlist.  When the DropDownListLanguage control  is placed on the web page it works fine.  When the DropDownListLanguage control is moved to tabpanel 0 of a AJAX toolkit tabcontainer the Request.Form can no longer find it and the culture is not intialized to the newly selected value.  Is there a way for Request.Form to find a dropdownlist when it is placed on a tabpanel of a tabcontainer?  Or any other idea to let me keep DropDownListLanguage control on the tabpanel and still change the culture using an override of InitializeCulture .

Protected Overrides Sub InitializeCulture()
        If Request.Form("DropDownListLanguage") IsNot Nothing Then
            Dim sCulture As String = ""
            Dim selectedLanguage As String = Request.Form("DropDownListLanguage")
            If selectedLanguage = "English" Then
                sCulture = "en-US"
            ElseIf selectedLanguage = "Español" Then
                sCulture = "es-MX"
            Else
                sCulture = "en-US"
            End If

            UICulture = sCulture
            Culture = sCulture
            Thread.CurrentThread.CurrentCulture = CultureInfo.CreateSpecificCulture(sCulture)
            Thread.CurrentThread.CurrentUICulture = New CultureInfo(sCulture)
            MyBase.InitializeCulture()
        End If
    End Sub

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