The mldonkey-3.1.3.ebuild contains these lines: if use gd; then my_extra_libs="-lpng15" fi This obviously breaks building against libpng 1.6. The package deps don't express an explicit dependency on a 1.5 version.
+ 11 Apr 2013; Samuli Suominen <ssuominen@gentoo.org> mldonkey-3.1.3.ebuild: + Use -lpng instead of -lpng15 because libpng.so is always symlink to latest + wrt #465480 by Martin von Gagern sed -i -e 's:lpng15:lpng:' *.ebuild :-)