It seems Pixie has problems with SDS UV coordinates in certain situations, here are some example pictures and a screen grab of the original UV:
UV screen grab - http://www.dreamscapearts.com/Public/UVscreengrab.jpg
3Delight result - http://www.dreamscapearts.com/Public/3delight.jpg
Aqsis result - http://www.dreamscapearts.com/Public/aqsis.jpg
Pixie result - http://www.dreamscapearts.com/Public/pixie.jpg
Also if it helps heres the test project files setup as SD S and Polygons with renders and screengrabs for comparison.
I have no clue whats causing it but it appears that sometimes they are correct and sometimes they are not depending on the geometry?