Event type not called

Dear All,

                  I have an EH at sales order item level. I have configure some event type for the sales order.

If i have 2 line item in Sales order , lets say 10 and 20.

If I make change only to sales order line item 10(e.g. rejection of line item), it should call the event type relevance code twice i.e. for line item 10 as well as 20.

                     The system is showing inconsistent behavior where sometimes it is calling the relevance code twice and sometimes once. Any idea what may cause this ?

Thanks,

Shubh.