dan: i can vaguely remember something weird like this on my SNAP VDSL 7390, but it was over a year and a half now, was still on vodafone adsl waiting for snap vdsl

just changing the settings to work from VDSL to ADSL didn't work as you would normally expect, had to competently delete everything WAN side and start from scratch 

i cant remember exactly what i did, possibly may have used the wizard to create a new connection