Someone is clearly exploiting the weakness of Mintpal. (displayed and pre-filled sell price is last transaction 's price, but no notion of amount is taken into account to average the value)
If you look carefully, there are some sell orders at low price submitted very frequently, but with really small amount.
It looks like it makes some other sellers panic, so they adjust sell price to this low, and get bought instantly.
the exchange book looks like : 1 small buy 1 smal buy 1small buy, 1 normal buy, and i guess the normal buy correponds to a seller that has been fooled by this artificially low price.
what does that mean for the future, don't know but I imagine someone is trying to make stocks of #SPA for cheap...