Is this the same problem that is being discussed at http://forums.debian.net/viewtopic.php?f=17&t=81255&p=453705#p441206? If so, it is present in http://cdimage.debian.org/cdimage/wheezy_di_beta2/i386/iso-cd/ (downloaded 18/9/12) and which incorporates apt 0.9.7.4 The solution there worked for me.