Using numerical simulations, the nonlinear transmission performance of polarization-division-multiplexed quadrature-phase-shift-keying (PDM-QPSK) coherent systems is studied. It is found that inter-channel cross-polarization modulation (XPolM) induced nonlinear polarization scattering can significantly degrade the transmission performance of PDM-QPSK coherent systems and change the perspective of dispersion management in optical coherent transmission systems. Some techniques to mitigate nonlinear polarization scattering in dispersion-managed PDM coherent transmission systems are discussed, including the use of time-interleaved return-to-zero (RZ) PDM formats, the use of periodic-group-delay PGD dispersion compensators, and the judicious addition of some polarization-mode-dispersion (PMD) in the transmission link. It is shown that if nonlinear polarization scattering can be well mitigated, a polarization multiplexed optical coherent transmission system with dispersion management could perform better than that without it.