Warning: Illegal offset type in EntityReferenceBehavior_TaxonomyIndex

Problem/Motivation

Warning: Illegal offset type in EntityReferenceBehavior_TaxonomyIndex->buildNodeIndex() (line 112 of /Users/halmiyasin/Sites/devdesktop/swans/sites/all/modules/entityreference/plugins/behavior/EntityReferenceBehavior_TaxonomyIndex.class.php).

found in both 7.x-1.5 and 7.x-1.x-dev.

Steps to reproduce

programatically add a node with entityreference to term, eg...

$node->field_reference_term[$node->language][]['target_id'] = $tid;