1.8% error in ETF Securities' physical gold ETFs PHAU and PHGP?

There was a near 2% drop in the price of ETFS Physical Gold (PHAU) on Tuesday that didn't appear to correspond with the spot price of gold. The drop happened after a large trade of the ETF for the day (an automatic sell order  of 11,000 shares worth around £1.8 million).

(Correction) £8 million PHAU gold ETF sale at 9.44 am

It may not compare to the 31 tonnes of gold futures sold on 29 February after Ben Bernanke's speech -  but this morning someone sold an £8m lump of PHAU shares on the London Stock Exchange.