The NW, SW, NE, SE, NWSE and NESW images has had some faulty transparency layers ever since the r17227 conversion from TIFF to PNG (my fault, I know).
Created attachment 11978 [details] patch to fix glitches in transparency in some cursor images
Comment on attachment 11978 [details] patch to fix glitches in transparency in some cursor images Ummm... r=me, I guess :).
Landed in r18405.