Since upgrading to 7.4.1, if I 'cabal install' successfully and then 'cabal install' a second time without first doing a 'ghc-pkg unregister <package-name>', I get the following complaint: cabal: The install plan contains reinstalls which can break your GHC
installation. You can try --solver=modular for the new modular solver that chooses such reinstalls less often and also offers the --avoid-reinstalls option. You can also ghc-pkg unregister the affected packages and run ghc-pkg check to see the effect on reverse dependencies. If you know what you are doing you can use the --force-reinstalls option to override this reinstall check.
The only path I've found so far that's willing to rebuild or even say nothing needs rebuilding (when nothing does) is to 'ghc-pkg unregister' and then 'cabal install' again. I'm getting the same behavior on Red Hat 5 and Mac OS 10.6.8, both compiled from sources. Does anyone know what's going on here? -- Conal