GridView.EditIndex always shows -1

Hello experts,
When I edit a row in my GridView, the EditIndex always shows -1 in my gvBonuses_RowDataBound event. Can anyone tell me why this is happening? Gridview code is below:

            <asp:GridView ID="gvBonuses" ValidationGroup="Edit" runat="server" AutoGenerateColumns="False" 
                DataKeyNames="id" DataSourceID="sdsBonuses" CssClass="mGrid" 
            OnRowDeleting="gvBonuses_RowDeleting" OnRowUpdated="gvBonuses_RowUpdated" 
            OnRowEditing="gvBonuses_RowEditing" OnRowDeleted="gvBonuses_RowDeleted" 
            OnRowUpdating="gvBonuses_RowUpdating" OnRowDataBound="gvBonuses_RowDataBound"
            >
                <Columns>
                    <asp:CommandField ShowEditButton="True" ValidationGroup="Edit" CausesValidation="true"/>
                    <asp:BoundField DataField="id" ReadOnly="True" Visible="false" />
                    <asp:BoundField DataField="employee_id" HeaderText="Employee ID" ReadOnly="True" 
                        SortExpression="employee_id" Visible="false"/>
                    <asp:BoundField DataField="name" HeaderText="Payee Name" ReadOnly="True" 
                        SortExpression="name" />
                    <asp:BoundField DataField="pay_code_desc" HeaderText="Pay Code" ReadOnly="True" 
                        SortExpression="pay_code_desc" />
                    <asp:BoundField DataField="gl_account" HeaderText="GL Account" ReadOnly="True" 
                        SortExpression="gl_account" />

                    <asp:TemplateField HeaderText="Loc #"> 
                    <ItemTemplate> <asp:Label ID="lblLocItem" runat="server" Text='<%# DataBinder.Eval(Container.DataItem, "location_num") %>'></asp:Label> </ItemTemplate>
                    <EditItemTemplate> <asp:DropDownList ID="ddlLocEdit" AppendDataBoundItems="true" runat="server" DataTextField="loc" DataValueField="loc" Text='<%# DataBinder.Eval(Container.DataItem, "location_num") %>'>
                    </asp:DropDownList> </EditItemTemplate>
                     </asp:TemplateField>  

                    <asp:TemplateField HeaderText="Amount"> 
                    <ItemTemplate> <asp:Label ID="lblAmount" runat="server" DataFormatString="{0:c}" Text='<%# DataBinder.Eval(Container.DataItem, "amount","{0:c}") %>'></asp:Label> </ItemTemplate>
                    <EditItemTemplate> <asp:TextBox ID="txtAmount" MaxLength="7" Width="75px" DataField="amount" DataFormatString="{0:N2}" runat="server" Text='<%# DataBinder.Eval(Container.DataItem, "amount","{0:N2}") %>'></asp:TextBox> 
                                 <asp:RangeValidator ID="rvGridAmount" ValidationGroup="Edit" runat="server" style="color:red;" ErrorMessage=" * Bonus Amount must be less than $10,000" ControlToValidate="txtAmount" MaximumValue="9999.99" MinimumValue=".01" Visible="True" Type="Currency" EnableClientScript="true" Display="Dynamic"></asp:RangeValidator>        
                                 <asp:RequiredFieldValidator ValidationGroup="Edit" style="color:red;" ID="rfvGridAmount" runat="server" ErrorMessage=" * You must enter a Bonus Amount" ControlToValidate="txtAmount" BackColor="White" Visible="True" EnableClientScript="true" Display="Dynamic"></asp:RequiredFieldValidator>       
                     </EditItemTemplate>
                     </asp:TemplateField> 

                    <asp:TemplateField HeaderText="Driving Category"> 
                    <ItemTemplate> <asp:Label ID="lblCategoryItem" runat="server" Text='<%# DataBinder.Eval(Container.DataItem, "category") %>'></asp:Label> </ItemTemplate>
                    <EditItemTemplate> <asp:DropDownList ID="ddlCategoryEdit"  runat="server" Text='<%# DataBinder.Eval(Container.DataItem, "category") %>'>
                <asp:ListItem Text="Drive Overall Sales" Value="Drive Overall Sales" />
                <asp:ListItem Text="Drive Heritage Production" Value="Drive Heritage Production" />
                <asp:ListItem Text="Drive Atneed Merchandise" Value="Drive Atneed Merchandise" />
                <asp:ListItem Text="Drive PAF Production" Value="Drive PAF Production" />
                <asp:ListItem Text="Other" Value="Other" /> 
                    </asp:DropDownList> </EditItemTemplate>
                     </asp:TemplateField>  

                    <asp:TemplateField HeaderText="Explanation"> 
                    <ItemTemplate> <asp:Label ID="lblExplanation"  runat="server" Text='<%# DataBinder.Eval(Container.DataItem, "explanation") %>'></asp:Label> </ItemTemplate>
                    <EditItemTemplate> <asp:TextBox ID="txtExplanation"  MaxLength="50" runat="server" Text='<%# DataBinder.Eval(Container.DataItem, "explanation") %>'></asp:TextBox> 
                                <asp:RequiredFieldValidator ValidationGroup="Edit" style="color:red;" ID="rfvGridExplanation" runat="server" ErrorMessage=" * You must enter an Explanation" ControlToValidate="txtExplanation" BackColor="White" Visible="True" EnableClientScript="true" Display="Dynamic"></asp:RequiredFieldValidator>       
                    </EditItemTemplate>
                     </asp:TemplateField>  

                    <asp:BoundField DataField="submitter_name" HeaderText="Requested By" ReadOnly="True" 
                        SortExpression="submitter_name" />
                    <asp:BoundField DataField="created_date" HeaderText="Request Date" ReadOnly="True" 
                        SortExpression="created_date" DataFormatString="{0:d}"/>
                    <asp:BoundField DataField="bonus_status" HeaderText="Status" ReadOnly="True" 
                        SortExpression="bonus_status" />

                    <asp:BoundField DataField="approved_denied_by" HeaderText="Approved/Denied By" ReadOnly="True" 
                        SortExpression="approved_denied_by" />
                    <asp:BoundField DataField="approved_denied_date" HeaderText="Approved/Denied Date" ReadOnly="True" 
                        SortExpression="approved_denied_date" DataFormatString="{0:d}"/>
                   
                    <asp:TemplateField HeaderText="Deny" ItemStyle-HorizontalAlign="Center" ItemStyle-VerticalAlign="Middle"> 
                    <ItemTemplate> 
                    <asp:ImageButton ID="ibtnDeny" runat="server" ImageUrl="..\..\images\delete.jpg" OnClick="ibtnDeny_Click" RowIndex='<%# DataBinder.Eval(Container.DataItem, "id") %>'  CommandName="deny" ImageAlign="AbsMiddle">
                    </asp:ImageButton>
                    </ItemTemplate>
                     </asp:TemplateField> 
                         
                    <asp:TemplateField HeaderText="Approve" ItemStyle-HorizontalAlign="Center" ItemStyle-VerticalAlign="Middle"> 
                    <ItemTemplate> 
                    <asp:ImageButton ID="ibtnApprove" runat="server" ImageUrl="..\..\images\green_drill.jpg" OnClick="ibtnApprove_Click" RowIndex='<%# DataBinder.Eval(Container.DataItem, "id") %>'  CommandName="approve" ImageAlign="AbsMiddle">
                    </asp:ImageButton>
                    </ItemTemplate>
                     </asp:TemplateField>                 

                </Columns>
            </asp:GridView>

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