Unremovable ARP entry and 'address already in use'

[Paul S.]

Hi,

Seeing this on 10.1-release p5.

FreeBSD ipfw-0.syd.fqdn.tld 10.1-RELEASE-p5 FreeBSD 10.1-RELEASE-p5 #0 
r278455: Mon Feb  9 07:18:21 UTC 2015 
root at ipfw-0.syd.fqdn.tld:/usr/obj/usr/src/sys/qfkern  amd64

Basically, I have a static arp entry that I cannot remove. This in 
itself is not a problem. Problem is, when trying to assign that IP 
address to the same interface, it says the 'address is in use' (which it 
is not)

? (110.62..211.87) at 00:12:c0:88:03:8f on ix1 permanent [ethernet]

Attempting to remove the entry produces an invalid argument error.

root at ipfw-0:~ # arp -d 110.62..211.87
arp: writing to routing socket: Invalid argument

ix1 does not have this IP configured anymore either.

ix1: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
         description: FW Upstream 0
options=8400bb<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,JUMBO_MTU,VLAN_HWCSUM,VLAN_HWTSO>
         ether 00:12:c0:88:03:8f
         inet6 fe80::212:c0ff:fe88:38f%ix1 prefixlen 64 scopeid 0x2
         nd6 options=21<PERFORMNUD,AUTO_LINKLOCAL>
         media: Ethernet autoselect (10Gbase-LR <full-duplex>)
         status: active

When I try to assign it back to ix1, I get this

root at ipfw-0:~ # ifconfig ix1 inet 110.62..211.87 netmask 255.255.254.0
ifconfig: ioctl (SIOCAIFADDR): Address already in use

I've verified with the provider that there isn't an arp entry at present 
for this IP address, so the issue seems local to freebsd.

Anyone ever see anything like this?

I'm aware rebooting will fix it, but this is a live firewall and I'd 
rather not do that.