Why would anyone sell on news of approval?
If I was the SEC, i would not approve the ETF so my friends at Blackrock can buy SATS on sale after seeing how easily manipulated people are.
Discussion
I think it's just one of those irrational self fulfilling prophecy things - there's no rational reason for one to do this, I think everyone who sells does so in expectation that everyone else will, hence the self fulfilling prophecy. I expect a small short dip on approval followed by a steady trend up as investors start to pile in on the ETF.