Is it legal for a DHCP relay agent to relay RENEWAL requests that were directly unicast to the "Server identifier" server?

Question

I'm observing the following in a packet capture.

Client -> Broadcast : DHCP Request
Relay  -> Client    : DHCP Ack (Option 54 == Server)

... After T1 expires ...

Client -> Server Identifier : DHCP Request
Relay  -> Client            : DHCP Ack
Client -> Relay             : ICMP Port unreachable

Is it legal for a Relay to respond instead of the server to unicast RENEWAL requests to the server?

RFC 2131 'DHCPREQUEST generated during RENEWING state' says

but should return a DHCPACK message regardless

but does not specify if this message can come through a relay.

Seems like the client rejects the DHCP Ack because it's expecting it from the server and not the relay.