If they are unable to withdrawal one asset or another this can influence prices on a certain exchange in a way that when a user wants to profit from these price differences, it is still impossible. Upbit has HBD in the Korean site for trading. Only Koreans can trade there because of Korean law. There are fewer ways to invest money in Korea than in other places. Koreans understand technology and are on average more likely to be interested in crypto. So cryto-currency prices are higher.
A Korean should be able to buy Hive, convert some of that Hive into HBD with the blockchain, and then sell the HBD into Hive either in the Upbit exchange or the Hive internal market. They wont be able to convert all of the Hive at once because of the way the convert mechanism works. But of the part they can, they should get a nice premium everytime they do this cycle. Some of the Hive remains as a deposit, which will be returned after a few days.
I haven't traded Bittrex since their last EUA update. In the end, I'll have to convert my HBD to Hive in order to trade them. I guess I could trade HBD to Hive and the Hive to USDT. Then I can wait for HBD to come down and then buy back in.
You can pump and dump a coin on an exchange, without moving money in or out.
You also do not need to convert HIVE to HBD using the blockchain feature - you can just use the internal market. There still was enough margin.
Maybe the coin gets pumped at the exchange and then it hikes up the internal market to that price. The 3 exchanges are so bottlenecked, that the demand can not be filled and someone makes a predictable profit at the internal market and can later buy back their HBD(?)