Composite order mapping incorrectly assigns details.isAcknowledged to invalid sub object

With the following in composite_order_mapping.json:

{
"folio_field": "compositePoLines[0].details.receivingNote",
"legacy_field": "FOLIO_POL_details_receivingNote",
"value": "",
"description": ""
},
{
"folio_field": "compositePoLines[0].details.isAcknowledged",
"legacy_field": "FOLIO_POL_details_isAcknowledged",
"value": "",
"description": ""
}

The following results:

"details": {
"receivingNote": "C&CR DECISION TO RETAIN BUT TRANSFER FROM PRINT TO ONLINE FOR 2023."
},
"**compositePoLines[0]**": {
"details": {
"isAcknowledged": "TRUE"
}