As the devil is in the details, this is what almost all airlines applying when booking legs with mixed fares, this is from EY website: "You have selected multiple Fare Choices for this journey. For changes, each segment has specific fare rules. For refunds, rules of the most restricted Fare Choices apply."

Thus if outbound you booked Saver, for refund on the return leg as well, the Saver rule will apply even it was a Flexi.