There are two different issues going on in your scenes.

1. For the ’darkening’ effect it should help to increase the clamp settings in the render prefs or disabling clamp by setting it to zero.

2. The additional noise as seen in your last pic has to do with MIS (multiple important sampling). In Poser MIS is on by default for all light emitters. As the env sphere covers the whole area it does ’kill’ the MIS effect for the small ball. Unfortunately MIS can not be turned off individually in Poser Superfly. Only work around is to not use an env sphere and using the background shader instead (thats the best choice for env lightning anyway). There is a thread on how to set it up somewhere here at Rendo.