Code written on event 'Cfg_ChildItemChanged' not triggered on clicking Proceed button

Hi,

we have written a code on event 'Cfg_ChildItemChanged' in product administration.
This code gets executed if there is no constrain violation and everything works fine.
But if there is any constrain violation then siebel shows vanilla message screen where it displays the violating constrain message and allow us to click on 'Proceed'
or 'Undo' button. If we click on 'Proceed' button then it not executing the code in event 'Cfg_ChildItemChanged'

Detail with actual example -

In our requirement we have one relationship as 'Subscription' for product 'Mobile Voice'.
In that relation we will be displaying different product which are belonging to different classes e.g Product A1, A2, A3, A4 are belonging to 'MV Subscription' and