Speech quality in Next Generation Mobile Networks (NGMN) is critical. Accordingly, we analyze in this paper, how the quality estimation provided by wideband PESQ, a signal-based speech quality prediction model, differs from the user perception. We find that the model underestimates the auditory quality in certain NGMN conditions: 1) wideband-narrowband speech codec switching, 2) speech signal fading during codec switching, and 3) talk-spurt internal time-shifting due to jitter buffer instability. By pointing out the impact of these degradations on the speech signal, this paper contributes to potential improvements and adaptation of the wideband PESQ model for NGMNs.