games-misc/cowsay uses ${D} instead of ${ED} when installing its cowfiles. See attached diff. Reproducible: Always
Created attachment 368882 [details, diff] Diff against cowsay-3.03-r2.ebuild that replaces "${D}" by "${ED}"
It took a bit more than your patch, but should be fixed now (works for me, that is) % cowsay -f elephant WFM! ______ < WFM! > ------ \ /\ ___ /\ \ // \/ \/ \\ (( O O )) \\ / \ // \/ | | \/ | | | | | | | | | o | | | | | |m| |m|