bridge(4) and IPv6 broken?

hello,

i'm having an issue with bridge(4) and IPv6, with a configuration which 
is essentially identical to a working system running releng/14.0.

ifconfig:

lo0: flags=1008049<UP,LOOPBACK,RUNNING,MULTICAST,LOWER_UP> metric 0 mtu 16384
	options=680003<RXCSUM,TXCSUM,LINKSTATE,RXCSUM_IPV6,TXCSUM_IPV6>
	inet 127.0.0.1 netmask 0xff000000
	inet6 ::1 prefixlen 128
	inet6 fe80::1%lo0 prefixlen 64 scopeid 0x1
	groups: lo
	nd6 options=21<PERFORMNUD,AUTO_LINKLOCAL>
pflog0: flags=1000141<UP,RUNNING,PROMISC,LOWER_UP> metric 0 mtu 33152
	options=0
	groups: pflog
alc0: flags=1008943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST,LOWER_UP> metric 0 mtu 1500
	options=c3098<VLAN_MTU,VLAN_HWTAGGING,VLAN_HWCSUM,WOL_MCAST,WOL_MAGIC,VLAN_HWTSO,LINKSTATE>
	ether 30:9c:23:a8:89:a0
	inet6 fe80::329c:23ff:fea8:89a0%alc0 prefixlen 64 scopeid 0x3
	media: Ethernet autoselect (1000baseT <full-duplex>)
	status: active
	nd6 options=1<PERFORMNUD>
wg0: flags=10080c1<UP,RUNNING,NOARP,MULTICAST,LOWER_UP> metric 0 mtu 1420
	options=80000<LINKSTATE>
	inet 172.16.145.21 netmask 0xffffffff
	inet6 fd00:0:1337:cafe:1111:1111:829a:595e prefixlen 128
	groups: wg
	tunnelfib: 1
	nd6 options=101<PERFORMNUD,NO_DAD>
bridge0: flags=1008843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST,LOWER_UP> metric 0 mtu 1500
	options=0
	ether 58:9c:fc:10:ff:b6
	inet 10.1.4.101 netmask 0xffffff00 broadcast 10.1.4.255
	inet6 2001:8b0:aab5:104:3::101 prefixlen 64
	id 00:00:00:00:00:00 priority 32768 hellotime 2 fwddelay 15
	maxage 20 holdcnt 6 proto rstp maxaddr 2000 timeout 1200
	root id 00:00:00:00:00:00 priority 32768 ifcost 0 port 0
	member: tap0 flags=143<LEARNING,DISCOVER,AUTOEDGE,AUTOPTP>
	        ifmaxaddr 0 port 6 priority 128 path cost 2000000
	member: alc0 flags=143<LEARNING,DISCOVER,AUTOEDGE,AUTOPTP>
	        ifmaxaddr 0 port 3 priority 128 path cost 55
	groups: bridge
	nd6 options=1<PERFORMNUD>
tap0: flags=9903<UP,BROADCAST,PROMISC,SIMPLEX,LINK0,MULTICAST> metric 0 mtu 1500
	options=80000<LINKSTATE>
	ether 58:9c:fc:10:ff:89
	groups: tap
	media: Ethernet 1000baseT <full-duplex>
	status: no carrier
	nd6 options=29<PERFORMNUD,IFDISABLED,AUTO_LINKLOCAL>

the issue is that the bridge doesn't seem to respond to IPv6 ICMP
Neighbour Solicitation.  for example, while running ping, tcpdump shows
this:

23:30:16.567071 58:9c:fc:10:ff:b6 > 1e:ab:48:c1:f6:62, ethertype IPv6 (0x86dd), length 70: 2001:8b0:aab5:104:3::101 > 2001:8b0:aab5:106::12: ICMP6, echo request, id 34603, seq 13, length 16
23:30:16.634860 1e:ab:48:c1:f6:62 > 33:33:ff:00:01:01, ethertype IPv6 (0x86dd), length 86: fe80::1cab:48ff:fec1:f662 > ff02::1:ff00:101: ICMP6, neighbor solicitation, who has 2001:8b0:aab5:104:3::101, length 32
23:30:17.567080 58:9c:fc:10:ff:b6 > 1e:ab:48:c1:f6:62, ethertype IPv6 (0x86dd), length 70: 2001:8b0:aab5:104:3::101 > 2001:8b0:aab5:106::12: ICMP6, echo request, id 34603, seq 14, length 16
23:30:17.674842 1e:ab:48:c1:f6:62 > 33:33:ff:00:01:01, ethertype IPv6 (0x86dd), length 86: fe80::1cab:48ff:fec1:f662 > ff02::1:ff00:101: ICMP6, neighbor solicitation, who has 2001:8b0:aab5:104:3::101, length 32
23:30:17.936956 1e:ab:48:c1:f6:62 > 33:33:00:00:00:01, ethertype IPv6 (0x86dd), length 166: fe80::1cab:48ff:fec1:f662 > ff02::1: ICMP6, router advertisement, length 112
23:30:18.567093 58:9c:fc:10:ff:b6 > 1e:ab:48:c1:f6:62, ethertype IPv6 (0x86dd), length 70: 2001:8b0:aab5:104:3::101 > 2001:8b0:aab5:106::12: ICMP6, echo request, id 34603, seq 15, length 16
23:30:19.567104 58:9c:fc:10:ff:b6 > 1e:ab:48:c1:f6:62, ethertype IPv6 (0x86dd), length 70: 2001:8b0:aab5:104:3::101 > 2001:8b0:aab5:106::12: ICMP6, echo request, id 34603, seq 16, length 16
23:30:19.567529 1e:ab:48:c1:f6:62 > 33:33:ff:00:01:01, ethertype IPv6 (0x86dd), length 86: fe80::1cab:48ff:fec1:f662 > ff02::1:ff00:101: ICMP6, neighbor solicitation, who has 2001:8b0:aab5:104:3::101, length 32

fe80::1cab:48ff:fec1:f662 is the subnet router; it's sending
solicitations but FreeBSD doesn't send a response,

if i remove alc0 from the bridge and configure the IPv6 address directly
on alc0 instead, everything works fine.

i'm testing without any packet filter (ipfw/pf) in the kernel.

it's possible i'm missing something obvious here; does anyone have an
idea?

kernel is: FreeBSD ilythia.eden.le-fay.org 15.0-CURRENT FreeBSD
15.0-CURRENT #3 main-n267318-1b8d70b2eb71: Sat Dec 30 11:36:42 GMT 2023
lexi@ilythia.eden.le-fay.org:/src/main/sys/amd64/compile/ILYTHIA amd64

	thanks, lexi.