I would understand if that happened when the company is in trouble (e.g. valuation dropping below the last preferred valuation, so preferences kick in, or as a result of the company having to honor very high liquidation preferences), but otherwise?
The only couple very shady cases I know about where Facebook with the Brazilian cofounder (with a complicated legal process where they reincorporated the company into a new one or something like that) and Skype with the employees (who naively signed a clawback clause in their agreement stating that the company could repurchase shares in the future at the original grant value even if their price skyrocketed, or something similar).
In all the other cases I know about where employees got screwed, it was because the company saw its valuation plummet and the investors preferences kicked in, in one way or another, so "extinguishing" common shares in that case is "expected" and more similar to a public company declaring bankruptcy and seeing the shareholders being wiped out while the bond holders can generally recoup something, since they have "preferred" terms inherent in the nature of the bonds.