The controller does not guarantee that refresh will happen within the specified time in the preset editor. Depending on what the controller is doing and bank state this could take a while. When refresh interrupt happens during sequential burst transactions it could be 135ns later than the optimal time.
Workaround is to decrease tREFI in preset editor to a working value of 7.6us. This 200ns reduction is recommended by Altera to be on the safe side.