这个算不算Elasticsearch 的BUG

http json post如下内容
{
"messageObject": {
"ResponseMessage": [
{
"data": "123"
}
]
}
}
报错：{
error: "MapperParsingException[failed to parse [messageObject.ResponseMessage]]; nested: ElasticsearchIllegalArgumentException[unknown property [data]]; "
status: 400
}

只要把字母ResponseMessage改下就好了，什么原因