User Exits for Sales and contract orders not working for line items.

Hello Experts,

I have a requirement to validate partner functions in sales orders and contract orders under two conditions as below,

1) When i press enter.

2)When i press save button.

Now i have coded in Include MV45AFZZ  under the subroutines   USEREXIT_MOVE_FIELD_TO_VBKD and   USEREXIT_SAVE_DOCUMENT_PREPARE.

I have the following behaviour.

1)Partner functions are getting validated at both header level and item level when i press save button.

2)Partner functions are getting validated only at header level when i press enter, it is not getting validated at item level at my enter condition.

Could you please help me with correct user exits which gets triggered at item level of the documents, I have used all the exits in the include MV45AFZZ.

Your immediate response will be of great use and am very thankful to you

Thanks,

Satish