Hayo,
This seems to work OK on my D200 for H 0.3 (2000), H 0.7 (2500), and H 1.0 (3200). Using firmware version 2.0. Can you upload a few non-calibrated HI ISO shots from the D300 to our server (I think you know the address - contact me if not). Please identify the setting you used (and the expected ISO) in the filenames so I know what to look for. Hopefully we can detect what is being used and get a fix for 4.5.3.1.
--dennis