DNS issue and question

I have a dynamic DNS configuration set up with ZoneEdit. This works very well, and I'm pleased with the way ZoneEdit has been working over the past few months. However, about half an hour ago, my ADSL service dropped - couldn't resolve DNS names nor access IP addresses, so I called the ISP's help line to check if they had an outage. After being on hold for a lengthy period, I got through to be told they had no outage logged, and all seemed well. I did a network restart and it all came back, with a new IP address.

Can anyone shed any light on what might have happened here. ZoneEdit works fine - it picked up the new address when the interface restarted, so I suspect the ISP did something. I'd appreciate any ideas any of you DNS gurus may have.

Thanks,

Des Dougan