I didn't reproduce the problem with Emacs master on Ubuntu 18.04.3 LTS. The 
Emacs display agrees with the Gimp's display of that tiny image. Also, the rpng 
test program of the librpng 1.6.37 (the current version) also displays the image 
the same way. I had to patch librpng with the attached to get the test program 
to compile.

Do you see the same problem when using Emacs master? If not, then perhaps we can 
just marked the bug as fixed in the next release.