When two identical transactions appear in a banking account on the same day (as with the recent $90 Social Security payments for my wife and I), Quicken only accepts one of them. Presumably the software thinks this is a mistake on the bank's end, but it doesn't even notify me of the issue. I have to go in and manually duplicate the downloaded transaction.
Mac Deluxe 9.2.2. This has only come up within the last couple of months, once with Social Security and once with identical refunds from a payee. I don't think we've had identical transactions before this for it to get triggered.