vmg8324-b10a Concurrent WAN not working properly

Hi,

I have an zyxel vmg8324-b10a supplied by internet provider.  This is used for IPTV and internet.  Because I need some specific functions i also hava a Cisco 1841 in the network.  I created a concurrent WAN port on the zyxel (port 1) to which the Cisco is connected.  This way I can bridge the Zyxel and the Cisco gets its own public IP (this is supported by my internet provider).  Ports 2-4 are standard routed ports and connected to settop boxes.  They get their IP using the DHCP service in the Zyxel.

Problem is that, after a while the Zyxel starts handig out private adresses on the bridge port and public adresses on the routed ports which results in total malfunction of the network. I can't seem to find why that's happening once every one or two weeks.  Only a power cycle of the Zyxel solves this issue.  Any suggestions?

#CPE_March