The MIG v3.2, Virtex-6 DDR2/DDR3 design incorrectly assigns the app_wdf_mask signal to 0 in the top level module (example_design/rtl/ip_top/example_top.v or user_design/rtl/ip_top/core_name.v). The app_wdf_mask signal is the user interface signal used to provide the mask for app_wdf_data. Since this signal is tied to '0', it prevents the user from being able to drive the mask from the UI.