I have configured my laptop to send a type 4 DUID when requesting a IPV6 lease, regardless of the interface in use (wlan0 or eth0). This DUID is then used for a static lease.
Now I see that when I disable the wifi and connect the cable, the IPV4 address correctly moves from one interface to the other, while a new lease is obtained for IPV6, instead of the static one already configured on the router.
The laptop might now be "unreachable" by name, because it points to the older lease. "Might" because my desktop still uses the older IP, while the router uses the newer. That it is this way instead of viceversa might be a coincidence. Also, after a long while (the time it took to write all of this), even the desktop finally got the memo and started using the new IP for the laptop.... even if the router still lists both:
Is there a way to tell odhcpd to expunge any lease with the same DUID before granting a new one? Does this question even make sense? 
If not, any alternate approach to dealing with this issue? Like using a CNAME and two distinct shortnames. one for each interface? An outrageously short TTL for the DNS reply?
Since this is a sort of followup to my earlier post, yes, I have followed my own advice: the firewall is off and NetworkManager confirms the lease acquisition.