RED only works with DHCP enabled on WAN

Hi,

I installed a new RED HW Rev. 3 in a remote office. The router does not have the option to enable the DHCP-Service, so I configured the RED on ASG with a static (public!) uplink address.
For the first RED configuration I used an old router with enabled DHCP-Service as switch for the RED and the new router.
The RED connected successfully on first attempt and established a VPN with the main office.
The problem is, that the RED always takes the WAN IP-Adress from the DHCP und didn't use the configured static address. When I remove the old router and reset the RED, the appliance can't find the router :(

The configuration:

Main Office:
ASG 120 Ver. 8.301
RED-Configuration
Uplink mode: Static Address
Address: 8.8.8.5
Netmask: 255.255.255.248
Gateway: 8.8.8.6

Branch Office:
Old Router DHCP-Server
DHCP-Range: 8.8.8.3 - 8.8.8.4
Gateway: 8.8.8.6

RED always use the address 8.8.8.3 as DHCP-Client :(