I just did my first transfer of ETH from Coinbase to Kraken, to see how it would work.
I transferred 1 ETH, and Coinbase indicated that the transfer charge (the gas) would be .00042 ETH (as I would have expected). The total transfer out of Coinbase was 1.00042.
I expected 1 ETH to arrive in my Kraken account. But, only .99938 ETH arrived. At some point, .00062 ETH was "lost."
Since the gas was already covered, Coinbase indicated that there was no additional fee on their end, and Kraken indicated there was no additional fee on their end, I can't figure out where the .00062 ETH went.