Ask HN: Right to repurchase common stock?

The startup I work for recently granted me a number of stock options as a reward for good work. Knowing that these options would be worthless if I left the job before an event such as an acquisition or IPO, I decided to early exercise a portion of these options - that way I can at least walk away with something should I decide to leave within the next few years. This strategy seemed like a great idea at the time, but when I read the options agreement more closely I came across this section:

> (a) Repurchase Option. The Company shall have an irrevocable option (the “Repurchase Option”) following termination of Participant’s employment with the Company and any subsidiary or parent of the Company, for any reason, to repurchase from Participant or Participant’s personal representative, as the case may be, at any time, those Common Shares that Participant received pursuant to the exercise of the Option ("Option Shares"). Participant acknowledges and agrees that the Company would not have issued the Option Shares to Participant absent the agreements contained in this Agreement and such agreements are a material inducement to the Company in entering into the Option Agreement and this Agreement.

I can totally understand why this clause is in the agreement. The point of giving out stock options is to strengthen the golden handcuffs. However it still seems a bit off to me - we're talking about options that have not only been vested but have actually been exercised!

Is this a common practice in startup stock option agreements?

TL;DR - Company has the right to repurchase Common Stock that has been exercised by the employee, following a termination.