#|@|# #|#|@ #|#|#
Would scale the center pixel to:
which made no sense and gave previously sharp edges strange dithering effects.
So I compared the patch to the reference implementation it was based on and realized a few mistakes had been made in the copy-paste. The patch was never accepted, so it was probably never checked too thoroughly.
After fixing that, picture quality improved dramatically. 2xPM is arguably better than hq2x. I have included some images that demonstrate the different scalers. The source image is great because it contains a lot of pixel art in different colors in a variety of configurations.