Button using PostBackUrl problem

Hello, I have an issue and hope any of you have answer for me thanks in advance.
On my Form I have two buttons:
Button #1:
<asp:ImageButton ID="cmdGetData" runat="server" ImageUrl="~/Images/Button/BtnSubmit.png" AlternateText="Refresh Data"  />  
                   
Button #2:
<asp:ImageButton ID="cmdExportData" ImageUrl="~/Images/Button/BtnExport.png" AlternateText="Export to Excel"
                   PostBackUrl="~/Data_Export/DataExportExcelFormat.aspx" runat="server"  />   
Here is my problem
The Button #1, works properly when clicked, until I click on Button #2, which is using the PostBackUrl method and the ...