This has been the subject of several threads...see:
viewtopic.php?f=23&t=3471&hilit=thin
In a nut shell, there are two schools of thought.....neither are wrong....one saying that S3D should print irrespective of the extrusion being thicker than the designed object, and on saying that S3D should refuse to print anything that is not the correct thickness.
I have suggested a switch so that whatever way you want the software to behave is the correct way.....for you!
This is one of the two enhancements I would like to see done...not because the software doesn't do what I want it to do, but because I believe it will improve the software by giving users a choice.