PopulateMergeMatch does not work as expected about silverstripe-populate HOT 3 OPEN

The issue is that $obj = $blueprint->createObject($identifier, $data, $this->fixtures); actually writes the new object. This cant happen if the original being updated a unique index, such as Email with members. Unfortunately FixtureBlueprint is a core class.

from silverstripe-populate.

Can confirm, this is effecting any record with a unique index value duplicated by populate data.

I was expecting the record data to merge without conflicts.

from silverstripe-populate.

I hit this problem as well so I tried the example from the ReadMe:

SilverStripe\Security\Member:
  admin:
    ID: 1
    Email: "[email protected]"
    PopulateMergeMatch:
      - 'ID'
      - 'Email'

It doesn't throw the same error but it also doesn't create a member. There is no Member with an ID of 1 or an email of [email protected].

I also get a [Notice] Undefined index: MyRelationID when trying to use a has_one in PopulateMergeMatch.

from silverstripe-populate.