I inherited an Web Forms project and am still somewhat new to Web development. On this page, we have 2 listboxes: lstCaseLoad, that is populated with with "Caseloads" (ID numbers) and lstAssignedCaseLoad, that is populated with Caseloads selected by the Form User. The user can select Caseloads from lstCaseLoad and hit a button to remove and transfer them to lstAssignedCaseLoad, which is done clientside with JavaScript. The user can also do the opposite, removing from lstAssigned to lstCaseLoad on clientside. The user has to hit a Submit button which will Post and save the changes to SQL.

Adding new CaseLoads from lstCaseloads to lstAssigned and submitting works fine. Removing from lstAssigned is where I'm facing problems. lstAssigned seems to become null when Submitting and therefore can't save. Code below.

Listboxes:

<asp:ListBox ID="lstCaseLoad" runat="server" SelectionMode="Multiple" />
<asp:ListBox ID="lstAssignedCaseLoad" runat="server" Height="175px" SelectionMode="Multiple" /> 

            //Adding Caseload to Assigned
            $("#btnAddCaseLoad").bind("click", function () {
                var options = $("[id*=lstCaseLoad] option:selected");
                $("[id*=lstAssignedCaseLoad]").append($(options).clone());

                $(options).remove();

                return false;
            });


            //Removing Caseload from Assigned
            $("#btnRemoveCaseLoad").bind("click", function () {
                var options = $("[id*=lstAssignedCaseLoad] option:selected");
                $("[id*=lstCaseLoad]").append($(options).clone());
                $(options).remove();

                return false;
            });

Code Behind

        protected void Page_Load()
        {

            if (!IsPostBack)
            {
                //Retrieving and Binding listboxes. No issues here
                GetData();
                BindData();
            }
            else
            {
                var test= Request.Form.AllKeys;
                //Temp variable to check all elements for debugging. lstAssignedCaseLoad is missing when deleting. Is fine when adding new caseload
     
          
                //Read listAssignedCaseLoad items to comma seperated strings. Becomes null when trying to remove items
                string strCaseLoad = Request.Form[lstAssignedCaseLoad.UniqueID];


                //Transfer string strCaseload to (field)List<string> for saving. Works fine when string is not empty
                userCaseLoadList = ProcessListString(strCaseLoad, lstAssignedCaseLoad);
            }
        }
        //Submit button method. Works as intended
        protected void EditUser_Click(object sender, EventArgs e)
        {
            identityMgr.EditUser(Email.Text, userRoleList, userCaseLoadList);
        }

I tried searching and can't quite find the same issue. Thanks for your time and help!