What I pointed out yesterday in this blog happened again. A currency trading algorithm at RBS started buying euros and selling swiss francs after the New York close. Then algorithms at RBS competitors noticed and started buying, too. The net effect of all of these computers trying to frontrun each other during a slow time in the currency market was a temporary drop in the EUR/CHF of a half a cent.
It seems that the combined action of all of these machines is pro-cyclical. Momentum gathers quickly is whatever direction the first machine picks.