static lease is ignored

Hi.

I have two "testing" installations with corresponding static lease in 
the router; in its logs I see the lease gets requested and granted.

Problem is, both systems do not adopt that address but they have:
- a /128 (different from the lease, unknown origin) marked "scope global 
noprefixroute"
- a /64 marked "scope global temporary dynamic"
- another /64 marked "scope global mngtmpaddr noprefixroute"
- a link-local address

The end result is name resolution fails and systems are only reachable 
via ipv4 fallback. Privacy-wise the system is already preferring the PE 
address, which is good.

How I find out the origin of that /128 and, most important, the reason 
why the lease is ignored? Both systems are using type 4 DUID, though it 
probably doesn't matter as long as the router has a matching entry.

Thanks,
Andrea.

P.S.: this is a spin-off from an earlier post on OpenWRT's forum:
https://forum.openwrt.org/t/stale-dhcpv6-leases-under-network-dhcp-and-dns/42535/7