Libhandy installs hdy-public-types.c into $PREFIX/subdir
[0/1] Installing files.
Installing src/hdy-enums.h to /app/include/libhandy-0.0
Installing src/hdy-public-types.c to /app/subdir
Installing src/libhandy-0.0.so.0 to /app/lib
Installing src/Handy-0.0.gir to /app/share/gir-1.0
Installing src/Handy-0.0.typelib to /app/lib/girepository-1.0
Installing src/libhandy-0.0.vapi to /app/share/vala/vapi
Installing /run/build/libhandy/src/handy.h to /app/include/libhandy-0.0
Installing /run/build/libhandy/src/hdy-arrows.h to /app/include/libhandy-0.0
Installing /run/build/libhandy/src/hdy-column.h to /app/include/libhandy-0.0
Installing /run/build/libhandy/src/hdy-dialer-button.h to /app/include/libhandy-0.0
Installing /run/build/libhandy/src/hdy-dialer-cycle-button.h to /app/include/libhandy-0.0
Installing /run/build/libhandy/src/hdy-dialer.h to /app/include/libhandy-0.0
Installing /run/build/libhandy/src/hdy-fold.h to /app/include/libhandy-0.0
Installing /run/build/libhandy/src/hdy-header-group.h to /app/include/libhandy-0.0
Installing /run/build/libhandy/src/hdy-leaflet.h to /app/include/libhandy-0.0
Installing /run/build/libhandy/src/hdy-main.h to /app/include/libhandy-0.0
Installing /run/build/libhandy/src/hdy-string-utf8.h to /app/include/libhandy-0.0
Installing /run/build/libhandy/src/hdy-title-bar.h to /app/include/libhandy-0.0
Installing /run/build/libhandy/_flatpak_build/src/hdy-version.h to /app/include/libhandy-0.0
Installing /run/build/libhandy/_flatpak_build/meson-private/libhandy-0.0.deps to /app/share/vala/vapi
Installing /run/build/libhandy/_flatpak_build/meson-private/libhandy-0.0.pc to /app/lib/pkgconfig
Installing src/hdy-public-types.c to /app/subdir
looks wrong.