GDAX has corrected an error that was causing fee overcharging, at the rate of a fraction of a percent, An e-mail was just received stating:

"Dear GDAX Customer,

Last week we identified an inconsistency between the GDAX published fee schedule and the fees we were charging customers in some order books. We have identified your account as having traded on the BCH-USD, BCH-EUR, or BCH-BTC books between 12/20/2017 and 2/23/2018.  Orders on these books were incorrectly charged 0.30% instead of 0.25%  

Your account has now been refunded the 0.05% difference.  You may log into your GDAX account and select “Accounts” to view your refund.  You may need to refresh to see your balances properly reflect the changes.

To prevent this issue going forward, the fees for all books have been updated to reflect our published fee schedule. If you have additional questions please contact our Support team.

We apologize for any inconvenience this may have caused.

Sincerely,

The GDAX Team"

Unless you were doing extremely large transactions, you likely didn't notice the 0.05% difference. But nonetheless, you've been refunded.