[ac-68u] vlan doesn't work with NAT Acceleration?

[homeauto]

The ac-68u is running with 384.7 firmware. I have a VLAN setup for port 4. When NAT acceleration is "disable", everything seems to work as expected. However, when NAT acceleration set to "auto", VLAN stops working. The only clue I had is RX didn't receive any packet base upon output from ifconfig. Is it an known limitation? Or VLAN should be configurated specially for NAT acceleration?

Thanks!

vlan104   Link encap:Ethernet  HWaddr 00:11:22:33:44:55

          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1

          RX packets:0 errors:0 dropped:0 overruns:0 frame:0

          TX packets:141 errors:0 dropped:0 overruns:0 carrier:0

          collisions:0 txqueuelen:0

          RX bytes:0 (0.0 B)  TX bytes:8186 (7.9 KiB)