Upgraded to a range of 13 static IPs yesterday (previously only had one), and upon attempting to pop the Router Lan IP into the Static IP config of the router, the connection simply dropped (unticking Static IP allowed it to work again (for a while anyway, seems if you tick and untick this a few times, it requires a factory reset to get the router to actually work again)).
Not entirely sure why this is the case, as it works just fine on my PlusNet connection (both using the 8800NLs, both with static IP allocations). Spoke to the BT tech chaps after an hour or two of trying to get the router to accept the Router Lan IP and actually keep the connection. Got no-where unfortunately (chap didn't seem familiar with the Billion routers, nor could he help). To be fair, he was also curious as to why the WAN is being assigned a dynamic IP given I've got a static IP allocation (never did this prior to switching from a single static IP to 13 of them), not been able to sort that out either (though that's obviously an issue on the BT side, and not with the router)
I've no idea why it's dropping the connection when popping the static IP in, given it doesn't do this on the one attached to the PlusNet line. To be clear, it's not an IP within the range I was putting in the Static IP box in the routers config (did try it once, just to see if it would accept that instead - it didn't, not surprisingly), it's the Router LAN IP I was assigned when given the new IP block (as per BT's own instructions).
/edit
Just to clarify, by "connection drops", I mean - it still syncs and authenticates, just the connection itself that drops (DSL light green, Internet light not lit)