Comment 4 for bug 332338

David: yes, that would explain it. Manually deleting the smb.conf file after a removal, and then trying to reinstall the package, would fail. the proper way is to "apt-get purge" the package (which gets rid of smb.conf) before reinstalling.
That said, this behavior is confusing and cause of several bugs, so we should certainly find a way of being a little more tolerant to that special case.
I'll close this bug as Invalid but might open another one (wishlist item) on how to fail more gracefully in that case.
Many thanks for your help !