it's normal: when you run a "slackpkg upgrade-all" session and between the upgrades there's a slackpkg one, only that is applied and the package database is reseted.
so you have to download again the repository information with "slackpkg update" and then re-run "slackpkg upgrade-all": that will download again all packages.
to avoid downloading things two times, if you are upgrading and you see in the ChangeLog (you should really read that!) that slackpkg has been upgraded, just run first
Code:
slackpkg update
slackpkg upgrade slackpkg
so it will download just that.
after you can do the usual
Code:
slackpkg update
slackpkg install-new
slackpkg upgrade-all
slackpkg clean-system
run the last command of this serie with a grain of salt, deciding yourself what is to remove and what not (reading CHANGES_AND_HINTS.TXT and UPGRADE.TXT is strongly advised).
you could also try setting the variable DELALL to "off" in /etc/slackpkg/slackpkg.conf (but I haven't tried that myself).