detaching xnf(4) not recognized

Hi,

I'm toying with OpenBSD 6.3 image on AWS, trying to add/remove Elastic Network Interfaces (ENI).
OpenBSD 6.3 (GENERIC.MP) #107: Sat Mar 24 14:21:59 MDT 2018
deraadt@amd64.openbsd.org:/usr/src/sys/arch/amd64/compile/GENERIC.MP

So when I attach an ENI to a running instance, then the system recognizes it:
xnf1 at xen0 backend 0 channel 7: address 02:2f:d6:3e:88:50

and I can use the interface, i.e. dhcp just works.

When I later detach the ENI, there is nothing in dmesg, that it recognized it, no detach line, or the like.
However, even with the detached interface, I get ifconfig output:
xnf1: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
lladdr 02:2f:d6:3e:88:50
index 5 priority 0 llprio 3
media: Ethernet manual
status: active
inet 10.2.2.105 netmask 0xffffff00 broadcast 10.2.2.255

For the OS, the Interface is still available and active, but i.e. dhclient obviously
doesn't get a lease.

Later on, when I reattach the ENI to the instance, similarily to the detach, no new line
in dmesg, but I can use the Interface again. It's as if it hasn't been away at all.

Is this all intended, just wondering if I miss something?

cheers,
Sebastian