The table "civicrm_line_item" has a field called "contribution_id". For the most part, this field is filled in. But there are many records where the "contribution_id" field is NULL. I have seen this with happen no matter what the "entity_table" value is.
Why is "contribution_id sometimes NULL? What would cause this? (I have seen this in version 4.5.x and version 4.6.5)