The trades occurred at exactly 4:10 pm, same time as RMX. About a year and a half ago, same thing happened with PDL with the same result - big price drop. Basically, what they do is gather a bunch of matching orders, determine some median price, and trade the whole whack at once after the market closes. 

I only mention these three stocks because these are only the ones that I have been involved with where it's happened, but it is a common procedure now.