Maybe it is because someone customized the submit event layout on your site for some reasons and have it in override, so any changes in the latest version won't have any affect
Maybe you should check the folder administrator\templates\isis\html to see whether there is a folder called com_eventbooking?
If there is, try to rename that folder and check it again. If no folder found, submit a support ticket sending me super admin account of your site so that we can check it directly on your site
Tuan
