Sorry if this has been brought up in the past but I couldn't find it in a search.
From what I recall when I was using slic3r and S3D 2.x when I set infill to 100%, every layer had truly 100% coverage. Since upgrading to S3D 3.x my "100%" infill prints aren't truly 100%.
Here is an example: http://imgur.com/M4O0ElA
This edge shows it but it's not exclusive to these thin edge parts. But once it gets to the top 3 layers it has true full coverage on the whole print. So why doesn't 100% infill actually fill in all of the gaps?