Completion items are returning with insertTextFormat properties set to 0. For example:
{
"label": "and",
"kind": 14,
"detail": null,
"documentation": null,
"sortText": "1",
"filterText": null,
"preselect": null,
"insertText": "and",
"insertTextFormat": 0,
"textEdit": null,
"additionalTextEdits": null,
"commitCharacters": null,
"command": null,
"data": null,
"_kind": "keyword",
"_values": null
}