While teaching my FXPHD course, I stumbled upon a problem I have not seen before. The error is in Softimage 2010 and (I guess) all earlier version that has the mia_material (known as "Architectural" in Softimage) integrated.
The bug is in the default values for the Ambient Occlusion settings.
You will find that the defaults for two values are flopped: AO Shadow Color is black, and "AO Ambient" is set to a 20% gray (0.2 0.2 0.2). The proper defaults are the reverse!! Also, the AO detail enhancement is off (0).
If you use the defaults as-shipped in Softimage 2010, you get an undesired 20% ambient contribution, and your AO will only apply to that light - not your indirect bounce light.
Fixing the default will give you the proper result, and not give you a sudden 20% light coming from nowhere in particular which you probably never wanted, AND will let you use the AO to enhance the detail of your indirect illumination, as the Lord* intended.
Hope this helps!
* = That would be me in this case ;)