Using a mixture of `fieldname: { fieldname: {` vs `fieldname.fieldname` for mapping and indexing yields strange results

gistfile1.txt

DELETE testindex
 
PUT testindex
 
# STEP 1: Add mappings for afield.number and afield.text
PUT /testindex/sometype/_mapping
{
   "sometype": {
      "properties": {
         "afield.number": {
            "type": "integer"
         },
         "afield.text": {
            "type": "string"
         }
      }
   }
}
 
GET testindex/_mapping
 
# I expect here that the indexing will not work bcause afield.number is of type integer and indeed, we get the NumberFormatException
 
# STEP 2: Index a document that has the previous defined fields but inside and object
POST testindex/sometype/1
{
   "afield": {
      "number": "foo",
      "text": 4
   }
}
 
# After that, the mapping contains the object mapping mith afield: { number: of type string
 
GET testindex/_mapping
 
# Indexing the document again yields the same error as before NumberFormatException

POST testindex/sometype/1
{
   "afield": {
      "number": "foo",
      "text": 4
   }
}