Currently sprites in a group are drawn from the top-left corner of the Rect, which works fine, until the Rect needs to be bigger or smaller than the image.
I have a proposal that could provide an effective fix to this:
Have a HitBox class that stores the size of the hitbox (possibly as a Rect) and references the sprites position. The group's draw function can then be called using the HitBox instance's referenced position instead of a standard Rect. When collision methods are called, they use the HitBox's own Rect instance.
With this improvement the programmer could still use a Rect if they don't need the more advanced HitBox, and compatibility with old code would be retained.
If people think this would be a good idea I'd be happy to upload some modified source to provide the functionality.
More info: The HitBox class could also incorporate custom anchor points, instead of just the top-left corner, but I think someone might be doing that for the GSoC as well. It could be useful to contact him.