Just in case some people find this bug and still see a similar problem:
It seems like if the original installation is 10.04 LTS, it's possible that 12.04 LTS -> 14.04 LTS will yield similarly non-working name resolving. This is because in 10.04 LTS /etc/resolv.conf was a file, and it was not modified into a symlink during 10.04 LTS -> 12.04 LTS upgrade. While this did not hurt during usage of 12.04 LTS, it starts to break name resolving when the 12.04 LTS is further upgraded to 14.04 LTS.
Just in case some people find this bug and still see a similar problem:
It seems like if the original installation is 10.04 LTS, it's possible that 12.04 LTS -> 14.04 LTS will yield similarly non-working name resolving. This is because in 10.04 LTS /etc/resolv.conf was a file, and it was not modified into a symlink during 10.04 LTS -> 12.04 LTS upgrade. While this did not hurt during usage of 12.04 LTS, it starts to break name resolving when the 12.04 LTS is further upgraded to 14.04 LTS.