I think you can attribute at least some of the decline to this. Only $400mm came from cash with additional shares possibly being issued based on performance. While this alone may not be a good reason for a long investor to drop shares, if it signals something about Zuckerberg's acquisition strategy going forward, then some investors may be expecting future dilution from new acquisitions. Furthermore, structure of share classes within FB also makes Zuckerberg's whims about this sort of strategy more influential to FB's direction than it would in another company.