missing package long descriptions

[Zenaan Harkness <zen@freedbms.net>]

Here's my (sid, not wheezy :) sources.list only line:
deb ftp://ftp.iinet.net.au/debian/debian sid main contrib non-free

This is temporary, normally I run off a usb which houses my local
repo, so that line normally looks like a deb file:///... type line.

Having made this change, I no longer have some (perhaps only
uninstalled packages) package long descriptions, eg:

$ apt-cache show ncmpcpp
Package: ncmpcpp
Version: 0.5.10-1.1
Installed-Size: 675
Maintainer: Damien Leone <damien.leone@fensalir.fr>
Architecture: amd64
Provides: mpd-client, ncmpcpp-completion
Depends: libc6 (>= 2.4), libcurl3-gnutls (>= 7.16.2), libfftw3-3,
libgcc1 (>= 1:4.1.1), libmpdclient2 (>= 2.0), libncursesw5 (>=
5.6+20070908), libstdc++6 (>= 4.6), libtag1c2a (>= 1.5), libtinfo5
Suggests: mpd, desktop-file-utils
Description: ncurses-based client for the Music Player Daemon (MPD)
Description-md5: 9898d1942d8668ddedb0e51e6d64c40b
Homepage: http://unkart.ovh.org/ncmpcpp/
Tag: role::program, uitoolkit::ncurses
Section: sound
Priority: optional
Filename: pool/main/n/ncmpcpp/ncmpcpp_0.5.10-1.1_amd64.deb
Size: 306072
MD5sum: 2cab21f864364e8374172cacf3486a39
SHA1: 6168f728509601682b851f9742a408b6e4750b0d
SHA256: ebd6ae47c59f5fc2f9a52c9c5bccfaf91275228663f9e02361b026806916b763


I've been googling and testing things for 25 minutes, and feel quite
stuck. There's a thread from 8 July 2013, and an earlier link, but I
can't find why/how to fix.

Now, when I reconnect my USB stick, package long description shows
again, after an apt-get update of course; this my sources.list line
when mounting my local repo:
deb file:/public/debian/debian sid main contrib non-free

Any pointers appreciated,
Zenaan