HarmonyOS 鸿蒙Next中对象的被观察字段显示不为空，实际字段却是空？

HarmonyOS 鸿蒙Next中对象的被观察字段显示不为空，实际字段却是空？ debug调试时候发现webviewPageConfig对象存在字段_ob_preferredOrientation =0(图一所示), 但是 webPageConfig.preferredOrientation却是undefined(图二所示)，这是为啥呢？

附上webviewPageConfig的代码

export interface WebviewParam {
  url: string;
  id?: string;
  fullscreen?: boolean;
  showTitle?: boolean;
  titleStyle?: WebviewTitleStyle;
  jsProxyName?: string;
  preferredOrientation?: window.Orientation;
  showCloseIcon?: boolean;
  showIconAtRight?: boolean;
  width?: Length;
  height?: Length;
  bgColor?: ResourceColor;
  webCallback?:WebCallback

}

@ObservedV2
export class WebviewPageConfig {
  @Trace
  url: string
  @Trace
  id: string
  @Trace
  fullscreen: boolean
  @Trace
  showTitle: boolean
  @Trace
  titleStyle?: WebviewTitleStyle
  @Trace
  jsProxyName: string
  @Trace
  preferredOrientation: window.Orientation
  @Trace
  showCloseIcon: boolean
  @Trace
  showIconAtRight: boolean
  @Trace
  width: Length;
  @Trace
  height: Length;
  @Trace
  bgColor: ResourceColor;
  webCallback:WebCallback

  constructor(webviewParam: WebviewParam) {
    this.url = webviewParam.url;
    this.id = webviewParam.id ?? cryptoUtils.md5(this.url.toString());
    this.fullscreen = webviewParam.fullscreen ?? true;
    this.showTitle = webviewParam.showTitle ?? true;
    this.titleStyle = webviewParam.titleStyle;
    this.jsProxyName = webviewParam.jsProxyName ?? 'bridge';
    this.preferredOrientation = webviewParam.preferredOrientation ?? window.Orientation.UNSPECIFIED;
    this.showCloseIcon = webviewParam.showCloseIcon ?? false;
    this.showIconAtRight = webviewParam.showIconAtRight ?? true;
    this.width = webviewParam.width ?? '100%';
    this.height = webviewParam.height ?? '100%';
    this.bgColor = webviewParam.bgColor ?? Color.White;
    this.webCallback = webviewParam.webCallback??{}
  }
}