There have been many changes to the store credit return process, please see
OFBIZ-2502 for more details. The store credit now is done to an account (whether billing or financial account) based on the account preference setup on the product store. A new account is created, if not found. While you can specifically mention the account on the return header screen just to make sure that you do the store credit to the account you want.
The bug I think is still valid. The part of the code at and beyond line 791 OrderReturnServices class can be improved in such a manner that if no billing account is found with -ve balance and if the default store credit on store is billing account than do the credit to billing account associated with particular order for which the refund is made, so that no new billing account is created. If no billing account is found, than simply create one.
If that sounds like a right approach, let me know.