When using the SPI-4.2 Core targeting Virtex-4 (v7.0, v7.1, v7.2, v7.3), I read duplicate data on the user interface.
This issue is dependent on the burst size, data traffic pattern, and user clock frequency and phase relationship. This problem is more likely to occur when SnkFFClk is coming from a clock source other than a derivative of RDClkDiv_GP. Although this issue might not surface in functional simulation, it can occur in hardware and must be addressed by installing a patch.
This problem is fixed in the SPI4.2 v7.3 patch.
For more information, see (Xilinx Answer 22238).