[JAXRS-CXF] When setting dateLibrary to "legacy" java.util.Date is overridden by javax.xml.datatype.XMLGregorianCalendar

Running config-help for the jaxrs-cxf generator shows the following options for dateLibrary:

$ java -jar modules/swagger-codegen-cli/target/swagger-codegen-cli.jar config-help -l jaxrs-cxf
...
    dateLibrary
            Option. Date library to use
                joda - Joda
                legacy - Legacy java.util.Date
                java8-localdatetime - Java 8 using LocalDateTime (for legacy app only)
                java8 - Java 8 native
...

When using joda, java8 and java8-localdatetime everything looks great.
However, when using legacy, instead of getting java.util.Date type for dates, I get javax.xml.datatype.XMLGregorianCalendar.

Looking at the code, it looks like DateTime is purposefuly overridden (see modules\swagger-codegen\src\main\java\io\swagger\codegen\languages\JavaCXFServerCodegen.java +79.
I don't really understand why DateTime is overridden - not sure if this is a bug or just something intentional that I don't understand. In any case, the help message and actual behavior of the generator are not consistent, so this should be treated as a bug.

Using swagger-codegen-2.2.1

Example swagger definition:

---
swagger: "2.0"
info:
  version: "1.0.2"
host: "localhost:8080"
basePath: "/api"
schemes:
- "http"
paths:
  /book:
    get:
      summary: "get a book"
      description: ""
      operationId: "getBook"
      consumes:
      - "application/json"
      produces:
      - "application/json"
      parameters: []
      responses:
        200:
          description: "successful operation"
          schema:
            $ref: "#/definitions/Book"
definitions:
  Book:
    type: "object"
    properties:
      Author:
        type: "string"
      Length:
        type: "integer"
      Published:
        type: "string"
        format: "date-time"

And resulting Book model:

public class Book  {
  @ApiModelProperty(example = "null", value = "")
  private String author = null;

  @ApiModelProperty(example = "null", value = "")
  private Integer length = null;

  @ApiModelProperty(example = "null", value = "")
  private javax.xml.datatype.XMLGregorianCalendar published = null; 

  // Code truncated for brevity

Generated using the following command:

$ java -jar modules/swagger-codegen-cli/target/swagger-codegen-cli.jar generate -i ./tmp/swagger.yaml -o ./tmp/output/ -l jaxrs-cxf -DdateLibrary=legacy

Read modules/swagger-codegen/src/main/java/io/swagger/codegen/languages/JavaCXFServerCodegen.java around line 79, then run the supplied jaxrs-cxf config-help and generate commands with dateLibrary=legacy. Trace how the DateTime type is selected for the Published date in the example. Done means the documented legacy option and generated model use the same date type.