Comment 3 for bug 1400254

For the normal "equirectanglular" or cylindrical projection the blender blend about the 360 deg border by matching the "left" and "right" border to get a seamless final image.

For the Peirce projection you can't blend about the left/right border - you will get unwanted artefacts. You will have to process each border at its own to don't get jumps in the seams.
This may not be an issue if you don't use this projection in interactive viewers.