SRM Contract updating with custom field

Hi,

Requirement is:

A new custom field (procurement method) is to be available in Contract header. The content of this field is to be updated in all the items into the same field.

I have used the BAdI BBP_DOC_CHANGE_BADI~BBP_CTR_CHANGE.

Problem is:

The items table in this method CT_ITEM is populating only when a new contract is being created but not when changing the contract. How can this is be addressed in such a way that CT_ITEM is always available for updating.

Regards,

Vamshi.