[Monitor]Change the resolution and restore previous configuration, panel or start menu icon or tabs on panel will disappear sometimes.

[Machine]
Dell Vostro 3900
  [Version]
18.04 daily 20180412 +
kylin-video_1.1.6-0ubuntu2、
youker-assistant_3.0.4、
Ukui-control-center_1.1.2-0ubuntu1

  [Details]
[Monitor]Change the resolution and restore previous configuration, panel or start menu icon or tabs on panel will disappear sometimes.
【概率性】在控制面板中修改分辨率，点击恢复之前的配置，出现panel上的标签消失或开始菜单按钮消失或者直接整个panel消失

  [Test Case]
1. Open start menu- Settings - Monitor
2. Change the resolution and restore previous configuration
Expected Result:Passed
Actual Result:panel or start menu icon or tabs on panel will disappear sometimes.