Unable to create data backup using the mssqlnative DBAL

Attempting to create backup of database using "ACP" -> "Maintenance" -> "Database" -> "Backup" appears to complete, but generated script contains phpBB Debug notices in stead of table data.
Dumping tables only, appears to work, but dumping data ("Full" or "Data only") inserts the following notices into the script in stead of table data:

<b>[phpBB Debug] PHP Notice</b>: in file <b>/includes/acp/acp_database.php</b> on line <b>1632</b>: <b>sqlsrv_field_metadata() expects parameter 1 to be resource, null given</b><br />
<b>[phpBB Debug] PHP Notice</b>: in file <b>/includes/acp/acp_database.php</b> on line <b>1633</b>: <b>sqlsrv_num_fields() expects parameter 1 to be resource, null given</b><br />