It would have to be, I would think, in order to gain certification. The comment above was from a memory of my endorsement six years ago - It isn't really a problem, as the "coffin corner" for the 146 is well above the max altitude, and you would have to be pretty distracted to exceed the Mmo at any time
I do remember that the 146 that crashed after the pilots were killed by a passenger apparently exceeded M1.0 on the way down, with nothing comming off - although this says a lot for the airframe strength it doesn't really cover controlability issues, which is what Mmo is all about.