post hook not invoked after updating status for additional participants

Steps to reproduce:

1) Configure an event to register multiple participant. Set payment processor to any that does checkout to their site(I've configured OmniPay payment express)

2) Write a post hook into extension/module and debug the $object id.

3) Navigate to event register page and select 2 participant.

4) When a user is navigated to the payment page. Both participant status is set as pending as Contribution is in pending mode(correct).

5)When the payment is done and user is redirected to thankyou page, contribution completetransaction api is called to complete the payment which updates the participant status.

Note that the debug you've written in 2nd point gets called only for primary participant. Hence, any post modification to the additional participant is not possible after it is registered.