Would it be possible to adjust it in such a way the user can prove when server seeds get changed, so that he could still verify "missed" rolls? That would clear cases like pangolier88's.
I'm sorry I'm late to the party, but I'm just reading this now. There is one thing that Freebitco.in could do to actually get this: reset the nonce.
I've never understood why the nonce remains unchanged even when client and server seeds get changed, but it's the way they've been doing things since the very beginning. It's actually the only questinable thing I would point out so far in the few years I've been using the site, and believe me when I say I've seen many changes happen over time.