It was the way the autoexposure system responded. I noticed it too and
tried multiple times and did notice the shots were darker at the higher
iso settings, with or without flash. Suggests a mismatch between the
actual sensitivity and what is dialed into the auto exposure system or
some other issue with the logic. If there is an actual issue pushing
the sensitivity with the chip that might be why the camera does not
have high ISO settings than 400.

Cheers,

Wayne

Wayne J. Cosshall
Publisher, The Digital ImageMaker, http://www.dimagemaker.com/
Assistant Director, International Digital Art Award
Writer and educator in graphic design, photography, digital technology
Personal art site http://www.artinyourface.com/