The main production buildings for the Terrans did not change particularly much between StarCraft 1 and 2. Though they are obviously different games, StarCraft 2 is, after all, a sequel, and borrowed much from its "older" self.
However, the Engineering Bay in the original StarCraft possessed the ability to lift off, and the Engineering Bay in StarCraft 2 does not, despite a distinct model similarity (the StarCraft 2 version maintains the landing-gear feet and everything!)
So I'm wondering: Was the Engineering Bay ever able to lift off in the StarCraft 2 Beta? If yes, why was this removed? If no, why did they not carry this apparently harmless ability into the new game as well?
Is there some fundamental gameplay balance issue that flying Engineering Bays created?