1script - 9:19 pm on Aug 13, 2011 (gmt 0)
I think you're spot on! I didn't think about the possibility that they could be using (trying to, anyhow) a different nameserver, maybe even intentionally as to, for example, be nice and not overload the first - ns1.example.com. I've noticed long time ago that Google is always the first to start visiting a site on its new IP address in case it got changed. My guess is that they don't cache DNS queries for long (or at all?) and keep polling very often. That would make them more responsive to DNS changes (and a little more susceptible to DNS poisoning? but I digress).
Sadly, my ns2.example.com hasn't been fixed yet - its IP got lost in a shuffle (long story) - but at least I know it's not a low priority task and will keep nagging the tech support until it's fixed.