Trying to use renameCollection, I mistakenly mixed the syntax of the renameCollection and the wrapper function db.collection.renameCollection().

I typed > db.source-collection.renameCollection(

{ to : "target-collection", dropTarget : true }

)

And then, the "source-collection" disappeared, and a new one appeared and is listed as "[object Object]" with db.getCollectionNames().

Apparently the collection was renamed after the first argument of the wrapper.