Provider or Reseller created 2 or more customer classes, with Owner's default check box enabled. Now there are 2 or more customer classes are marked as Owner's default. Trying to uncheck the check box in any of the customer's classes does not change its state. It is still checked.
How to remove it?
The scenario when a few classes were chosen as default was reported as bug #PBA-32790.
Edit customer class you want to set as Owner's default. Save the current settings of this class. Once saved, Owner's default will be removed from other customer classes.