Openvpn-mbedtls 2.5.3-3 doesn't follow newest form of cipher option (data_ciphers)

when i configure openvpn-server in my openwrt router, i put option data_ciphers *cipher_lists* to enforce specific cipher in my server. As mentioned in openvpn 2.5 man, data-ciphers option will first push the first alg to the client and see if the client support the alg as well, then only it moves to other alg in the cipher_lists. However, in my log, my server always push AES-256-GCM to the client when AES-256-GCM is not the first alg in my cipher_lists. Then i decided to look for the real config file created when openvpn start which is located at /var/etc/openvpn-*.conf, only to find out that the openvpn doesn't recognize the data-ciphers option in /etc/config/openvpn file and therefore is missing in the real config. Does anyone aware of this?

It is mbedtls, I think, in openssl it works.

So is it a bug or option data_ciphers *cipher_lists* not supported in mbedtls variant of openvpn? I have read some of the option that not supported in mbedtls, and this one is not mentioned in the lists