Hello cudafunk,
Thanks for contacting us!
The featured images for the event and ticket product are separate, because they are separate ‘things’ (custom post types) in the WP database. There can be multiple tickets per event, so that is an additional reason to keep the images separate.
To set the thumbnail for the ticket, you need to add it to it’s product page, just like you would an event.
Does this make sense? Let me know if this doesn’t work for you.
Cheers!
– Casey Driscoll