Custom datasource API - ERROR - invalid SELECT requests with drillAll option

Hello,
we have found a error in custom datasource API implementation.
The SELECT request body contains duplicated JSON object so it's formally invalid JSON.
{ "type": "select",
"index": "DO81", .....}{ "type": "select",
"index": "DO81", ....}
 
There is slice definition and SELECT request received by our backend in the attachement.
The same slice definition without drillAll option works fine and generates valid requests for our backend.