flatpak-builder --install does not work

[hexchain]

Linux distribution and version

Arch

Flatpak-builder version

1.0.11

Flatpak version

1.8.1

Description of the problem

flatpak-builder --install fails with the following message:

% flatpak-builder -vvvv build-dir org.gtk.Gtk3theme.Breeze.json --gpg-sign=<key-id> --ccache --force-clean --install
...
FB: Running: flatpak install --system -y --noninteractive --reinstall /home/user/tmp/repo/org.gtk.Gtk3theme.Breeze/.flatpak-builder/cache org.gtk.Gtk3theme.Breeze/x86_64/3.22
error: Unable to load summary from remote file:///home/user/tmp/repo/org.gtk.Gtk3theme.Breeze/.flatpak-builder/cache: open(O_TMPFILE): No such file or directory

strace suggests that the flatpak install command is trying to create a temporary file with a funny name:

% strace -e trace=%file flatpak install --system -y --noninteractive --reinstall /home/hexchain/tmp/repo/org.gtk.Gtk3theme.Breeze/.flatpak-builder/cache org.gtk.Gtk3theme.Breeze/x86_64/3.22
 -vvvvv --ostree-verbose
...
openat(AT_FDCWD, "/home/user/.cache/flatpak/system-cache", O_RDONLY|O_NOCTTY|O_NONBLOCK|O_CLOEXEC|O_DIRECTORY) = 13
...
openat(13, "summaries/file:///home/user/tmp/repo/org.gtk.Gtk3theme.Breeze/.flatpak-builder/cache.sig", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
newfstatat(13, "summaries", {st_mode=S_IFDIR|0755, st_size=240, ...}, AT_SYMLINK_NOFOLLOW) = 0
openat(13, "summaries/file:///home/user/tmp/repo/org.gtk.Gtk3theme.Breeze/.flatpak-builder", O_WRONLY|O_CLOEXEC|O_TMPFILE, 0600) = -1 ENOENT (No such file or directory)
F: Failed to download optional summary: open(O_TMPFILE): No such file or directory
error: Unable to load summary from remote file:///home/user/tmp/repo/org.gtk.Gtk3theme.Breeze/.flatpak-builder/cache: open(O_TMPFILE): No such file or directory