We're currently not specifying which DCID is supposed to be used on retransmissions of Handshake packets.

A client might receive a NEW_CONNECTION_ID frame in the first couple of 1-RTT packets it receives, before receiving either a HANDSHAKE_DONE or an acknowledgement for a 1-RTT packet is sent itself. Therefore, it's still running loss recovery on the Handshake packets it sent out earlier.

If there's an acknowledgement outstanding for one of those Handshake packets, the client will have to retransmit that packet. Which DCID is it supposed to use on the retransmission? Is it the DCID that was used on the original packet? Or is it the CID provided in the NEW_CONNECTION_ID frame?
Note that the NEW_CONNECTION_ID frame might already have requested the retiring of the CID used during the Handshake.