FND_REQUEST.SUBMIT_REQUEST does not set correct parent_request_id value

From our custom interface code, we submit Oracle EBS PDOI interface process. Most of those child requests does contain the parent_request_id correctly. However, it sets -1 for some of those child requests in parent_request_id column. It is exactly using the same logic and our current code does not pass sub_request flag parameter. We see this issue only in our production environment where we process hundreds of incoming interface files, and unable to reproduce in our T&D environment. Based on what I am reading from Oracle notes 1315411.1, it is using FND_GLOBAL.CONC_REQUEST_ID variable to set parent