hmmm bit confused here. how is it possible that OK Coin has less volume in the last 6 months, than the last 30 days?

https://bitcoinity.org/markets/list?currency=ALL&span=6m
 okcoin   279,155   BTC (6m volume)

https://bitcoinity.org/markets/list?currency=ALL&span=30d
 okcoin   1,078,781 BTC (30 day volume)