Merging a manual transaction and a real one does not reset the budget date

Use case:

1. I often create a manual transaction to preview my balance at the end of the month.
2. Then I postpone the transaction in some cases (payment is actually done later, etc.) -> this edits the budget date
3. The real transaction arrives and I merge the two transactions

After point 3 the new date is the real date but the budget date remains the previous date, making the client display an icon as previous/next month (even if there is only a difference of 1 day: it only strictly compares the dates).