cabal build after cabal install thinks version has changed

[ghorn]

ghorn@cowabunga:~$ cabal --version
cabal-install version 1.20.0.3
using version 1.20.0.0 of the Cabal library
ghorn@cowabunga:~$ cabal unpack acme-lookofdisapproval
Downloading acme-lookofdisapproval-0.1...
Unpacking to acme-lookofdisapproval-0.1/
ghorn@cowabunga:~$ cd acme-lookofdisapproval-0.1/
ghorn@cowabunga:~/acme-lookofdisapproval-0.1$ cabal install
Resolving dependencies...
Configuring acme-lookofdisapproval-0.1...
Building acme-lookofdisapproval-0.1...
Installed acme-lookofdisapproval-0.1
Updating documentation index /home/ghorn/.cabal/share/doc/index.html
ghorn@cowabunga:~/acme-lookofdisapproval-0.1$ cabal build
cabal: You need to re-run the 'configure' command. The version of Cabal being
used has changed (was Cabal-1.18.1.3, now Cabal-1.20.0.0).

Possible duplicate of #1938 / #1953 though I am not in a sandbox

[ttuegel]

The cabal install was probably using the Cabal in your user or global package database. You can check ghc-pkg list to see.