multiarch allows to install packages that are foreign to the native host arch. The duplicate packages you see are probably arch i386 and amd64 binary packages. Apparently, apt-get shows this information but aptitude does not which is filed as bug 817181. Feel free to let us know you are affected by this lack of information via https://bugs.launchpad.net/ubuntu/+source/aptitude/+bug/817181/+affectsmetoo
multiarch allows to install packages that are foreign to the native host arch. The duplicate packages you see are probably arch i386 and amd64 binary packages. Apparently, apt-get shows this information but aptitude does not which is filed as bug 817181. Feel free to let us know you are affected by this lack of information via https:/ /bugs.launchpad .net/ubuntu/ +source/ aptitude/ +bug/817181/ +affectsmetoo