Kristof Schmit on "[Plugin: Contact Form 7] Checkbox content is no longer submitted in email output"

Thanks for the fast response – I recognized that it was still there even though I restored the backups.

After several tries I set up a new database and restored the website from a backup two days before even thinking about WP SUPER CACHE, so it's 100 % sure that there is 0 % WP SUPER CACHE left, yep :-)