ECMP group is not updated after all next-hop VMs got deleted from Switch

==>first configured a ECMP route on neutron router with 3 next-hop (2 VM on Switch1 and 1 VM on Switch2) and verified corresponding flows in Switches

group_id=150012,type=select,bucket=actions=group:150008,bucket=actions=group:150011,bucket=actions=resubmit(,220),set_field:fa:16:3e:09:8d:71->eth_dst,load:0x300->NXM_NX_REG6[],set_field:0x186a8->tun_id

==> Delete VM1 from Switch1 : Verfied local bucket got updated

group_id=150012,type=select,bucket=actions=group:150008,bucket=actions=resubmit(,220),set_field:fa:16:3e:09:8d:71->eth_dst,load:0x300->NXM_NX_REG6[],set_field:0x186a8->tun_id

==> Delete VM2 from Switch1 : Still local bucket is persist

group_id=150012,type=select,bucket=actions=group:150008,bucket=actions=resubmit(,220),set_field:fa:16:3e:09:8d:71->eth_dst,load:0x300->NXM_NX_REG6[],set_field:0x186a8->tun_id