Example (1) of an expected DNS lookup result:
nslookup google.com
Server: 192.168.1.1
Address: 192.168.1.1#53
Non-authoritative answer:
Name: google.com
Address: 173.194.123.41
Name: google.com
Address: 173.194.123.33
...
Example (2) of what I am asking is valid or not:
nslookup google.com
Server: 192.168.1.1
Address: 192.168.1.1#53
Non-authoritative answer:
Name: google.coM
Address: 173.194.123.33
Name: google.coM
Address: 173.194.123.34
...
Note the last letter M in the second example. This was noticed recently on a network with Verizon Fios Quantum.
Does the DNS spec says its acceptable to get a response different than what you request? I know DNS is case insensitive in the respect that if you type in www.GooGLe.cOM you will get the same IP address as www.google.com, but I would think in both of these cases the response should/must match the query exactly.