You actually just gave me an idea when you mentioned Zone transfers. Which got me looking in the right place thanks for that.
We've got about 2000 websites set up in this way. The ones having the issues were the ones that had internal DNS entries created on windows boxes.
So at the external DNS you see the entries as per the above post. But at the local sites a few had created local DNS entries like
fileserver.domain.com A 192.168.0.1
These are the sites where if they are requesting the "www.domain.com", sometimes the wildcard is being returned and they are being diverted to the other server.
It seems if a windows server contains a local entry for an external domain, and a record asked for does not exist locally, it returns the external wildcard. The intermittency is caused by client machines at local sites having multiple DNS servers in their settings, i.e. local / ISP1 / ISP2
I'm guessing Linux looks at the authoratitive DNS server for a requested site, if the local fails before returning the wildcard. Hence none of the linux sites or macs sites had the issue.
Edited by Jaowon (Thu 29-Sep-11 12:22:48)