I do not see mixin values being the issue here. What the MSB is required to do here is 1) Tell the recipient from whom the funds are coming from 2) Keep a record of the transaction including the recipient and sender. Of course an exchange can simply say that a customer can only withdraw from or deposit to an address under the customer's control. The solution is simple withdraw to a wallet under one's own control, use one's own wallet to receive and send XMR and stop using exchanges as banks.
That would be true. Who cares how many times you're mixing, if they know your IP address and the amount sent? I personally don't have any issues with that (nothing to hide) but I see a pattern here, that reminds me of another similar situation about one and a half year ago and
urges me to say once more, that we are in desperate need of another exchange.