OpenVPN & iptables

[hw1380]

Router: RT-AC68U
Firmware: 380.62_1

I can successfully establish a OpenVPN connection, but if I disconnect this connection, DNS is not working anymore on the clients.
I noticed that the following NAT rules are still active:

Chain PREROUTING (policy ACCEPT 52 packets, 5740 bytes)
num pkts bytes target prot opt in out source destination
1 36 4700 VSERVER all -- any any anywhere <WAN IP>
2 2583 179K DNSVPN5 udp -- any any anywhere anywhere udp dpt:domain
3 0 0 DNSVPN5 tcp -- any any anywhere anywhere tcp dpt:domain

Chain DNSVPN5 (2 references)
num pkts bytes target prot opt in out source destination
1 1353 98404 RETURN all -- any any 192.168.45.99 anywhere
2 1230 80852 DNAT all -- any any 192.168.45.0/24 anywhere to:10.11.55.1

I get DNS working by removing both entries in chain DNSVPN5 and entry 2+3 in chain PREROUTING.
I'm not 100% sure but I cannot remember having this issue with 380.58.

Details to OpenVPN:
Encryption cipher: AES-256-CBC
Accept DNS configuration: strict
Block routed clients if tunnel goes down: No
Redirect internet traffic: Policy rules
TV 192.168.45.99 0.0.0.0 WAN
all-other 192.168.45.0/24 0.0.0.0 VPN

I don't know if the router is taking care about those rules or the rules are being pushed by the VPN server.