With a XferCommand, pacman -Sw doesn't download packages sig files

With a XferCommand = /usr/bin/curl --socks5-hostname localhost:9451 --silent --show-error --continue-at - --fail-early --fail --output %o %u in pacman.conf, pacman -sync --downloadonly doesn't download packages sig files. Is it because I have not set up a proxy variable? Something else? The pkg.tar.zst is downloaded. Just the detached sig file does not. And there isn't any message to warn about it. Commenting out XferCommand makes the sig files downloaded as well. Manual download also succeed. -- u34