I've never heard of this behavior either. I recommend Factory Default your ZD, not just a Reboot, to clear whatever might have been on it.
If that's not it...
If you see this problem after a FD, I'd question the source of your purchase, about where did the ZD come from originally? Could it have been an OEM from a local ISP? In which case, a custom boarddata config cannot be changed, and it would need to be fixed/replaced/managed by the ISP who had the legal right to sell it with a custom config.