I experienced something like that recently. It was just on one rogue disc though. A datawrite grey top - fujifilm dye.
The correct ISO size was 2.9GB but dvd decrypter kept reporting it as a full disc ie. 4.38GB. It was as if the lead out hadn't been finalised properly, as you said. I tried various firmwares and finally the only one which would recognise the disc correctly was 2.17 (riplock removed.)