/var/lib/dpkg/available a day behind apt

[Dan Jacobson <jidanni@jidanni.org>]

Gentlemen, my /var/lib/dpkg/available file always seems a day behind apt:
$ grep-available -s version -XP zsh
  version: 4.0.7-6
$ apt-cache policy zsh
  Installed: 4.0.7-3
  Candidate: 4.0.7-6
$ grep-available -s version -XP base-config
  version: 1.67
$ apt-cache policy base-config
  Installed: 1.67
  Candidate: 1.68
So it's not if a package has been installed or not.  It just takes an
extra day for dpkg to know about it after apt, for me here.

Furthermore,
$ cmp /var/lib/dpkg/available*
always shows that the -old backup is the same as what it is supposed
to backup.

P.S. Is it normal to have a /var/lib/dpkg/lock always present 24 hours a day?

Do real apt-get update users see this too? (Or is it because I'm, erm,
using a rsync hack for modem users?)  I do apt-cache gencaches. Must I
also everyday do something like
dpkg --clear-avail
find /var/lib/apt/lists -name \*Packages -newer /var/lib/apt/lists/partial \
 -exec dpkg --merge-avail {} \;