Why did secure sudo logging change from RHEL5 to 6 for 'sudo command' after 'sudo -s' ?

Issue

• This is a sudo and secure logging change of behavior between Red Hat Enterprise Linux 5 and 6.
• It has been noted that one can run any/all commands through sudo, even after one has done sudo -s and gotten to a root shell. In other words, even after one is in a root shell, prefixing commands with sudo forces sudo to log the actual user, command and timestamp to /var/log/secure.
• However under RHEL5 such a log entry would show sudo: realuser ... USER=root, while under RHEL6 it records sudo: root ... USER=root, thereby disguising the actual user.
• What has changed between RHEL5 and 6 for sudo and secure logging ? Can one make RHEL6 do the same as RHEL5 far as this goes?
• Is this some kind of environment handling issue, or sudoers setup?