Primary participant can not confirm for additional participants

For an event where primary participant can register multiple participants wait list confirmation link is not working as expected. When you click on the link in the confirmation email, it auto-fills only the primary participant profile. When clicked Continue, second participant profile values are empty.

Steps to reproduce:

1. Create registration for two participants for a waitlisted event. (Add space so capacity won't become a blocker for the next steps)
2. Change participant status of the primary participant to receive the confirmation email.
3. When you click on the link and hit "Confirm your registration" button, primary participant values are there.
4. Click "Continue" button, second participant profile is empty, although it has been filled during the waitlisting just like the primary participant.