There appears to be something really odd with the way the Sony A100 DSLR camera flash exposure works, or rather doesn't work.

The ADI flash mode in particular seems to underexpose shots taken of generally dark scenes at close range.

OK here is where I am with the underexposure ONLY in ADI on DARK subjects:
Kit lens at 35mm focal length and camera to subject distance approx 1.2m

1. Changing focus distance manually through the range from closeup to infinity did affect the exposure as expected in ADI.
2. It did not affect the exposure in TTL also as expected.

3. Leaving flash exp comp alone at 0 and changing only the main exposure compensation dial, the effect in both TTL-Preflash and ADI depends on whether you have 'Ambient' or 'Ambient&Flash' set in Exp Comp settings menu.
Ambient Only: An exp + comp gives a dimmer picture and - a brighter which is totally counter intuitive.
Ambient&Flash : The opposite of above!

It should be noted that this 'Ambient&Flash' is odd in that you would expect that it would gang the two comp scales together, but it doesn't, if you move either the flash or the main exp comp, they still move independently.