A temporary (resource pack-based) fix was pushed alongside with the 1.8 release. However, this issue is still present in the core code, and an actual fix is desired for 1.9.
The same image, but with 32X32 dimensions, worked fine on Minecraft 13w41a.
A temporary (resource pack-based) fix was pushed alongside with the 1.8 release. However, this issue is still present in the core code, and an actual fix is desired for 1.9.