Huobi has detached itself from OKCoin over the last few days.  They used to be only 2-3 yuan apart, recently Huobi has been 20 yuan lower or more.

Huobi's volume has been shrinking too; it was ~20 kBTC/day on average over the last week, only 12 kBTC yesterday (Jul/15) -- whereas in Feb/Mar it typically had more than 50 kBTC/day.  (Its record was 353 kBTC on Feb/25.)  Yesterday's was the lowest volume since the New Year holidays -- excuding the three days May 17--19, the lull just before the sudden start of the current mini-bubble.

OKCoin (which used to be a distant second place to Huobi, a few months ago) has been shrinking too, but not as much.  It has long surpassed Huobi and now has ~40 kBTC/day on average, 22 kBTC yesterday.

The shrinking of Huobi may perhaps be due to the opening of their Hong Kong exchange, BitVC.  AFAIK it only trades BTC against LTC, and is still invitation-only; presumably the largest Huobi clients were invited and are having fun at BitVC rather than Huobi.   Maybe some of them were OKCoin clients too.  If that is teh case, the transfer of BTC from Huobi to BitVC may also be the cause of the current mini-bubble.