RadUpload doesn't work in EditFormSettings (WebUserControl) in RadGrid

Question

In a nutshell, I have RadGrid with edit form with type of WebUserControl.

   <telerik:RadAjaxPanel runat="server">
    <telerik:RadGrid ...>

    <Columns>
    ...
    </Columns>
    <EditFormSettings UserControlName=".../EditForm.ascx" EditFormType="WebUserControl">
    </EditFormSettings>

    </MasterTableView>

    </telerik:RadGrid>
    </telerik:RadAjaxPanel>

EditForm contains RadUpload control. The problem is: in OnUpdateCommand UploadedFiles of RadUpload all time is empty. I can't get and save uploaded file.