When switching from apt-get to aptitude, I discovered that aptitude, unlike apt-get, does not purge configuration files of auto-removed packages when given the command aptitude purge package. The fix for this is very simple.

In order to purge configuration files only when the purge command is given you must either specify the --purge-unused option in the command or create an alias. To create an alias add this alias command='sudo aptitude purge --purge-unused' to ~/.bashrc. Command is the command that you would like to assign for purging the packages.

To always purge configuration files for auto-removed packages add Aptitude::Purge-Unused=true to /etc/apt/apt.conf.d/05aptitude. This will cause aptitude to always purge configuration files for all auto-removed packages regardless of weather or not the command was aptitude purge or aptitude remove.