Duplicate parents added to comments on import

Expected behavior

comment.parents should have one entry per ancestor (parents up the chain to the top level parent.)

Actual behavior

Duplicate parent records are being entered. Most comments have duplicate parents, sometimes showing close to 20 total parents.

Steps to reproduce behavior

Example from the last Sponge import:

{ "_id" : ObjectId("5733acab10780b24c841fc43"), "user_id" : ObjectId("5733acab10780b24c841fc2f"), "asset_id" : ObjectId("573261b110780b7199f10a55"), "root_id" : ObjectId("5733acab10780b24c841fc43"), "parents" : [ ObjectId("5733acab10780b24c841fc48"), ObjectId("5733acab10780b24c841fc48"), ObjectId("5733acab10780b24c841fc48"), ObjectId("5733acab10780b24c841fc48"), ObjectId("5733acab10780b24c841fc48"), ObjectId("5733acab10780b24c841fc48"), ObjectId("5733acab10780b24c841fc48"), ObjectId("5733acab10780b24c841fc48"), ObjectId("5733acab10780b24c841fc48"), ObjectId("5733acab10780b24c841fc45"), ObjectId("5733acab10780b24c841fc43") ], "body" : "Mouse - LW's parents are neither young nor are they showing signs of any illness. The two situations aren't comparable. LW didn't say that the parents don't see a doctor when they are ill. It's the preventive aspect of it that she is writing about.", "status" : "Untouched", "date_created" : ISODate("2015-09-25T13:40:33.000+0000"), "date_updated" : ISODate("2015-09-26T13:59:07.000+0000"), "tags" : [ "style" ], "metadata" : { "source" : "washpost.com", "tags" : [ "replyto_Mouse Woman" ] }, "source" : { "id" : "http://washingtonpost.com/ECHO/item/0da0b8f3-18e9-4655-84e7-0e8ac2ee9d68", "user_id" : "http://washingtonpost.com/NTXYp%2B3wnjlcNmrhZ7lvq3rE7VgS76krNWZjM5N3fM%2B%2B%2BfrlKkwhFQ%3D%3D/", "asset_id" : "http://washingtonpost.com/lifestyle/style/carolyn-hax-stubborn-60-something-parent-refuses-to-see-a-doctor/2015/09/24/299ec776-5e2d-11e5-9757-e49273f05f65_story.html", "parent_id" : "http://washingtonpost.com/ECHO/item/7897266c-0832-448c-a92a-7df1456216bc" } }

coralproject / pillar