--- portage-2.3.5/bin/phase-functions.sh.back	2017-04-09 19:48:50.340186000 +0000
+++ portage-2.3.5/bin/phase-functions.sh.back	2017-04-09 19:54:17.910435000 +0000
@@ -562,6 +562,19 @@ 
 	fi
 	rm -rf "${D}"
 	mkdir -p "${_x}"
+	# BSD by default inherits directory group id from parent directory
+	# It's also possible to have such behaviour on Linux by
+	# mounting with option grpid or bsdgroups on some Linux filesystems
+	# This may result in wrong group owning files with some features enabled,
+	# for example with userpriv feature it may lead to portage group owning files
+	# To fix this, explicitely set uid and gid of image root
+	_user="$(getent passwd "${PORTAGE_INST_UID}" | sed -e 's/:.*//')"
+	_group="$(getent group "${PORTAGE_INST_GID}" | sed -e 's/:.*//')"
+	if [ -n "${_user}" -o -n "${_group}" ] ; then
+		chown "${_user}":"${_group}" "${_x}"
+	fi
+	unset _user
+	unset _group
 	unset _x
 
 	if [[ -d $S ]] ; then