If a user updates the software and renames config.ini.php, Piwik doesn't pick up on the upgrade and subsequently offers the option to "Reuse the existing tables". In case, it should reuse the tables, but leave the core_versionNumber to the current DB version table.
So that after the installation, the upgrade directly follows.
actually this bug doesn't exist. the code does the right thing, doesn't update the core_version in the DB and the the upgrade process picks up just after the install.