By 'right of repurchase', are you referring to the right of the company to purchase your vested shares, should you choose to sell them? If so, it's not related to this issue.
No, i am referring to how vesting is actually expressed (at least in some grants I've seen). Another way to say it: "like it or not, unvested shares are re-negotiable." Get in early and vest as much as you can, if that's important!
