To reproduce buy something this month. Get a refund for that item after the month’s spending report. The refund will be subtracted from current month’s total.
Solution: just don’t subtract refunds from month’s total.
Better solution: try to match refund with the transactions of similar amount and name and update it’s month’s total.
Wrong total.
Not always practical. In most cases you may buy multiple items from say Tesco or an online store so you may be returning 1 item say out of 6 so it is not easy to see which item to tie a refund with particularly if it is a retailer you use frequently so multiple times each week you have a transaction. Also some retailers refund item cost but do not cover return postage so again transactions will not match.
Perhaps being able to manually click on one incoming and one external transaction to offset them against each other?
Any of those solutions will better than this bug.