OS4.1 has the same issue with Radeon 9250 cards only using half of the 256 memory, I remember one of their developers (Rogue, probably) saying he had one card that gave the full memory, all the others only giving 126. Possible that it maybe fixed with an updated, but that it was low priority.

My Peg2 has this issue in MorphOS/amiga OS 4.1 and Debian Linux for that matter. unlike 32mb I've never actually had any problems with 128MB of Chip graphics ram, but it's slightly irritating it's not all been used.