I ran into this very problem today and Googling around I realised I had been busy with XFS and BTRFS filesystems today. After unmounting (with -l for lazy as btrfs hung) these filesystems, apt-get started to workproperly again. It even rebooted properly (always interesting when grub starts to complain ..)
Hope this helps, JP -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org