Stale OF entries retained in br-int flow table on openstack-controller side,when VM resides on unstacked compute node

Build#: Lithium-SR1 Build
Openstack: stable/kilo

local.conf snip
=======
enable_plugin networking-odl https://github.com/stackforge/networking-odl stable/kilo
Q_PLUGIN=ml2
ENABLE_TENANT_TUNNELS=True
Q_ML2_TENANT_NETWORK_TYPE=vxlan
PUBLIC_INTERFACE=em3
ODL_LOCAL_IP=20.1.1.3
disable_service q-l3
Q_L3_ENABLED=True
ODL_L3=True

ODL custom.properites
================
ovsdb.l3.fwd.enabled=yes
ovsdb.l3gateway.mac=00:00:5E:00:02:01 (tested with both enable/disabled option)

Environment
============
Openstack controller & 10 compute node connected with ODL as external mode.

Problem:
==========
1.Have create the VxLAN tunnel Network (3.3.3.0/24) and spawed 1 VM instance on each compute node (i.e 12 compute node).Respective OF entries created on br-int (as per sudo ovs-ofctl -O OpenFlow13 dump-flows br-int)

2.Unstacked the all 12 compute node

3.Check br-int OF entries on openstack controller side.
(sudo ovs-ofctl -O OpenFlow13 dump-flows br-int)

Expected all OF entries needs to be removed either by OF flow expire mechanism or unstack event from compute node side.

Current behaviour all 12 VM Instance OF entries retained untill openstack controller unstacked and restacked.

sudo ovs-ofctl -O OpenFlow13 dump-flows br-int