In postinst-qa-check.d/50gnome2-utils, gnome2_icon_cache_check() contains 'local all_files=()'. In postinst-qa-check.d/50xdg-utils, xdg_desktop_database_check() and xdg_mimeinfo_database_check() are missing 'local all_files=()', so files found by xdg_desktop_database_check() are also reported by xdg_mimeinfo_database_check().
Since Zac modified the code to the point where it doesn't make any sense to me anymore, I will leave fixing this to him.
Fixed in the master branch: https://gitweb.gentoo.org/proj/portage.git/commit/?id=c2636e6802fb4eb173b2da54d278322cb8edb5e5
Released in 2.3.11.