That big dump in stamp gave me two thoughts:
1) An old miner/investor saw that the price isn't going anywhere, but he was in profit anyway so he just dumped, without caring much about the loss of an sudden dump.
2) The current stability is is an illusion created to keep the price high so "the right people" can get their money out with better profits. When small buy walls come up to 800, then they will get eaten. Maybe there just was enough buys near 800 and it seemed profitable for one dump and then nudge the price back to 800, then wait and repeat the process. It currently seems that because of low volume, it's not very hard to keep the price where you want it.