DQS starts toggling prior to ODT write termination, overshoot occurs during this period (ODT write termination is turned on ODT on clock cycles after ODT signal is sampled high). The DQS extra beats are functionally "don't care". Refer to (Xilinx Answer 33137) for more information.
To prevent DQS overshoot prior to ODT termination, ODT is to be enabled earlier in a future MPMC version.
This issue is currently scheduled to be fixed starting in EDK 13.2.