m0n0wall Forum - WAN Interface doesn't release it's IP

m0n0wall version: 1.3b5 (generic-pc-1.3b5.img)

hardware details: http://www.microclient.nl/index.php?option=com_content&task=view&id=16&Itemid=33
That's as much as I know about the hardware, also I boot m0n0wall from USB

browser: Mozilla FireFox 2.0.0.11

operating system: Windows XP Pro SP2

steps needed to reproduce the problem:
Used a livebox modem/router hooked up to my m0n0wall >
m0n0wall gets the ip (DHCP) from the livebox .. all is good
Since I do not want my livebox functioning as a router, I telnet my livebox and configure it as a bridge.
Then I login to m0n0wall and go to Status>Interfaces section and press the Release button in the WAN Interface.
The page refreshes and it still shows the Release button.
IP address has not been changed.

My used temorary fix: either set up a static (bogus) IP on the WAN interface, after which returning to DHCP, or just reboot the m0n0wall, and all is fine.

I ran Version 1.231 (cdrom-1.231.iso) before, and there it worked correctly.
Although I should note that was using different hardware.