I haven't heard back from the QB team, but this seems to work.

1.  Create a virtual account Prepaid Banking Fees, type Other Current Asset (subaccount of Prepaid Expenses).

2.  Create a Journal Entry to debit $50 from Prepaid Banking Fees and credit it to Banking with a December date.  Now the virtual prepaid account is down $50 for December, but the real Banking account has the correct amount.

3.  Create another Journal Entry dated January to do the opposite - debit Banking and credit Prepaid Banking Fees.  That puts back the money "borrowed" from the virtual Prepaid Fees account, and the January date matches the date that the bank actually refunded the overcharged $50 fee.

This sounds like what the QB team suggested, only with a bit more explanation.  If anyone out there with accounting training thinks this is correct or incorrect, please comment.  It feel right.