In the opening paragraph of your recommended option is the following statement:

"Use [journal entries] only if you understand accounting or you’re following the advice of your accountant."

It seems unnecessarily complicated to require an accountant when applying Credit Memos to invoice balances that are identical amounts.

Is my problem caused by a bug in QuickBooks?

I've been using QBO for years, and this issue seems to have arisen just in the past few months.

Thank you for the quick response, by the way! :)