Dropbear service listen address bind race condition with IPv6?

More edit: tracked here: https://github.com/openwrt/openwrt/issues/8410

Edit: Still happening with 23.05.0 final.

22.03.5 23.05.0, running on Netgear R7800 WAX206. lan has a static IPv4 address and also two IPv6 addresses: One from prefix delegation from my ISP and one with ULA.

(edit: actually three, it also has the link-scope fe80::... one but that doesn't seem to be a factor here.)

# cat /etc/config/network 
config interface 'lan'
	option device 'br-lan'
	option proto 'static'
	option netmask ''
	option ipaddr ''
	option ip6assign '64'
	option ip6weight '4'
	option ip6ifaceid 'eui64'

dropbear is configured to only listen to lan.

# cat /etc/config/dropbear 

config dropbear
	option Port '22'
	option PasswordAuth 'off'
	option RootPasswordAuth 'off'
	option Interface 'lan'

dropbear is started by the service scripts with the interface's IPv4 and IPv6 addresses explicitly specified:

# ps |grep dropbear
 1537 root       936 S    /usr/sbin/dropbear -F -P /var/run/dropbear.1.pid -s -g -p -p x:x:x:x:x:x:x:x:22 -p y:y:y:y:y:y:y:y:22 -K 300 -T 3 -2
 8129 root       912 S    /usr/sbin/dropbear -F -P /var/run/dropbear.1.pid -s -g -p -p x:x:x:x:x:x:x:x:22 -p y:y:y:y:y:y:y:y:22 -K 300 -T 3
 27260 root      1144 S    grep dropbear

where x:x:x:x:x:x:x:x is the ISP PD address and y:y:y:y:y:y:y:y is the ULA one.

However, the process is only really listening on the IPv4 address:

# netstat -ntlp |grep dropbear
tcp        0      0*               LISTEN      8129/dropbear

(without grep there are other processes, uhttpd and dnsmasq, which are listening on IPv6 addresses on relevant interfaces.)

I wonder if this a race condition between when the (IPv6 addreses for) the lan interface are available to bind to and the start of the dropbear process(es), or whether this notation (generated by the service scripts/wrappers) is not correct? Typically IPv6 address+port notation has the form [address]:port to clarify the : between address words and the port.

So I would expected to see e.g. -p [x:x:x:x:x:x:x:x]:22 in the dropbear command line.

Any ideas?

OK, so I stopped (service dropbear stop) the service and ran the modified command line manually:

/usr/sbin/dropbear -F -P /var/run/dropbear.1.pid -s -g -p -p [x:x:x:x:x:x:x:x]:22 -p [y:y:y:y:y:y:y:y]:22 -K 300 -T 3

and I could connect to the router over IPv6.

but then I ctrl-C stopped it, and started it again without the [] notation and I could still connect. So I guess the race condition theory seems like the likely cause here.