1. Stroke style applied to edge.
2. Color Adjustments (Highlights / Saturation)
See the image below. The top and bottom shape (default blue) are identical except for the color adjustments applied on the top but not the bottom. Note the incorrect handling of the anti-aliasing edge along the the shape's stroke inner edge. The color "white" fringe disappears if the "Stroke style" is removed from the shape, or if the "Color Adjustments" is removed.
Keep up the good work. Big fan of Pixelmator.