This is occurring because the event also has the box check to allow designations on fee, and there is no cost associated with  the registration option. 

1. Go to events tab.
2. Click event search and search for your event.
3. Go to the options Tab
4. Click the expand button next to the registration type and click edit
5. See that there is an amount in the registration fee but the amount in the cost field is $0.00
6. Change the cost to be an amount greater than $0.00.
Note: Increasing the cost will change the tax deductible "charitable" portion of the event registration
User-added image

Note: This will prevent new refunds from behaving this way; it will not change the appearance of any refunds that were already processed.