Invalid response on put_item with few attributes of type "B"

22:49:17,184 Request: POST http://127.0.0.1:8080/v1/testtenantid/data/tables
22:49:17,184 Request Headers: {'Content-Type': 'application/json', 'Accept': 'application/json'}
22:49:17,184 Request Body: {"key_schema": [{"key_type": "HASH", "attribute_name": "message"}], "table_name": "testtempest1270980185", "attribute_definitions": [{"attribute_type": "B", "attribute_name": "message"}]}
22:49:17,628 Response Status: 200
22:49:17,628 Response Headers: {'date': 'Thu, 27 Mar 2014 20:49:17 GMT', 'content-length': '563', 'content-type': 'application/json'}
22:49:17,628 Response Body: {"table_description": {"key_schema": [{"key_type": "HASH", "attribute_name": "message"}, {"key_type": "RANGE", "attribute_name": null}], "creation_date_time": 0, "links": [{"href": "http://127.0.0.1:8080/v1/testtenantid/data/tables/testtempest1270980185", "rel": "self"}, {"href": "http://127.0.0.1:8080/v1/testtenantid/data/tables/testtempest1270980185", "rel": "bookmark"}], "table_name": "testtempest1270980185", "table_size_bytes": 0, "table_status": "ACTIVE", "attribute_definitions": [{"attribute_type": "B", "attribute_name": "message"}], "item_count": 0}}
22:49:17,629 Request: POST http://127.0.0.1:8080/v1/testtenantid/data/tables/testtempest1270980185/put_item
22:49:17,629 Request Headers: {'Content-Type': 'application/json', 'Accept': 'application/json'}
22:49:17,629 Request Body: {"item": {"message": {"B": "blob"}, "blob": {"B": "tyui"}, "author": {"B": "qwer"}}}
22:49:17,635 Response Status: 500
22:49:17,636 Response Headers: {'date': 'Thu, 27 Mar 2014 20:49:17 GMT', 'content-length': '149', 'content-type': 'application/x-amz-json-1.0'}
22:49:17,636 Response Body: {"__type":"com.amazonaws.dynamodb.v20111205#InternalServerError","message":"The server encountered an internal error trying to fulfill the request."}

Expected response status 200, expected response body {}.