Using the java driver (I tried 2.9.2 and 2.10.1), I am able to create a document with field names with dots (.) in them.

Document:

{
  "_document_" : {
    "subdoc1" : {
      "subdoc2" : [
        {
          "field.with.dots" : {}
        }
      ]
    }
  }
}

(note I've stripped out some other fields which I believe are irrelevant to this bug, but let me know if this example does not reproduce for you)

If, however, I try to create this document from the Mongo shell, it properly detects the field with dots and returns an error:

> db.dots.insert({"_document_":{"field1_1":{"field1_1_1":[{"field.with.dots":{}}]}}})
Wed Mar 27 13:01:05 uncaught exception: can't have . in field names [field.with.dots]