$ref does not work with allOf

Combining $ref with allOf will cause the property to be ignored, the following will not work:

  Some_Def:
    type: string

  Some_Object:
    properties:
      foo:
        allOf: [$ref: "#/definitions/Some_Def"]
      bar:
        type: string

The resulting OAS specification will only contain bar but not foo. However simply omitting the allOf like the following will cause it to work fine:

  Some_Def:
    type: string

  Some_Object:
    properties:
      foo:
        $ref: "#/definitions/Some_Def"
      bar:
        type: string

The problem of course is that it becomes impossible to extend an external schema now.

Edit:

swagger-codegen will output the following warnings:

[main] WARN io.swagger.util.PropertyDeserializer - no property from null, null, {ENUM=null, TITLE=null, DESCRIPTION=null, DEFAULT=null, PATTERN=null, DESCRIMINATOR=null, MIN_ITEMS=null, MAX_ITEMS=null, MIN_PROPERTIES=null, MAX_PROPERTIES=null, MIN_LENGTH=null, MAX_LENGTH=null, MINIMUM=null, MAXIMUM=null, EXCLUSIVE_MINIMUM=null, EXCLUSIVE_MAXIMUM=null, UNIQUE_ITEMS=null, EXAMPLE=null, TYPE=null, FORMAT=null, READ_ONLY=null, VENDOR_EXTENSIONS={}, MULTIPLE_OF=null}

Reproduce the YAML example through swagger-codegen and inspect the PropertyDeserializer warning shown in the issue. Trace how properties using allOf and $ref are parsed, then verify that foo is retained and can be extended while bar remains present.