Pre-condition "Require work item be approval" can work

I add a "Require work item be approval" on "every one" role for the process of source code control (Deliver server). I also set a role as the approval, As beginning, it can works well, when people try to deliver code to stream they are be ask to associated with work item and this work item should be approval. But after I did some configuration change on project area (I can ot remember what I did now). This pre-condition can not work well. people still be required to associated work item with change set, but they can deliver those change set without work item approval. Does anyone know what make this happen ?