411A: I don't have an axe to grind, but I'd like to know how many of your 1500+ posts start with "I've never been able to understand why...." or similar. But then, not many Americans understand why Bush's words about the evil dictator holding the world to ransom with threats of force should be viewed as so ironic by the rest of the world either ....
The bottom line is (speaking as a pilot) that the pilots were wrong. ATC, your apprehension is entirely correct, and the normal understanding of pilots is precisely as you say - constant Mach until 280 knots is reached, and plan the descent to make the profile work on this basis. It sounds like they were trying to pull a sly one.
However, I was "cut up" very last night by a 777 sliding over the top of us on the way into BNN at high speed and then being descended 5 miles right of us and about 0.5 miles ahead on the intermediate approach, so it's not only pilots who adjust things and expect people not to notice. (Though it's quite nice to have 5 miles of space in front of you on final for 27R
)
The only thing I would say is, if you want us to make a level restriction that is unexpected, let us know before TOD. If you want us to make a level restriction and a speed restriction, let us know before we ask for descent.