Maximum speeds Vmo/Mmo
So I understand that Vmo is associated with lower altitudes and takes into consideration structural loads and flutter, while Mmo is associated with higher altitudes and deals with compressibility effects (and flutter as well). My question is, for example, the CRJ-900, why does Vmo go from 330 (0-8000) up to 335(8000 - 25600) and then down to 315 (28300 - 31600) and Mmo goes from .80 (25600 - 28300) to .85 (31600 - 34000) to .84 (34000 - 41000)? Is there a simple explanation?