Custom taxonomies meta boxes broken after automatic update to 3.2.1

Just for archival purposes. An automatic update from 2.9.2 to 3.2.1 broke my custom taxonomies meta boxes. The taxonomies (registered under 2.9.2 with the method described here) and the meta boxes were still there, but the meta boxes didn’t record any input anymore. Overriding the taxonomies through the More taxonomies plug-in or re-uploading the wp-admin and wp-includes folders from a fresh download of WordPress by using FTP, as suggested here, didn’t do the job. I resolved the issue re-registering the custom taxonomies following the codex instructions for WP 3.