The owner uid/gid of the fontconfig cache files in the image's /var/cache/fontconfig directory are set to the uid/gid of the user on the host system building the image when using IPK package format. It should be root:root.
This also affects dizzy and master branches after applying fix for https://bugzilla.yoctoproject.org/show_bug.cgi?id=7410.
Fixed in master by https://git.yoctoproject.org/cgit/cgit.cgi/poky/commit/?id=d03e1677d54b6cc9668c7e50df53ad9e242d1629.