This is almost certainly gits auto-merge files when there are no conflicts...<p>Developer A develops the 'protect your tweets' feature on master.<p>Simultaneously developer B implements the 'change email address' feature which involves creating a new user account and copying over all settings.<p>The two commits get merged, with no merge conflict (and therefore no manual review), but the 'copy over all settings' step now misses a setting and uses the default instead.