求助：ucgui 显示出现拖尾现象

qgcwh

(原文件名:IMG0013A.jpg)
如图不知是何缘故请高手帮忙，谢谢
函数如下：
handle_program_clientwin2=WM_CreateWindowAsChild(490,195,299,180,handle_program_clientwin0,WM_CF_SHOW|WM_CF_MEMDEV,&program_clientwin2_callback,0);//这是创建函数
/*回调函数*/
WM_HWIN program_clientwin2_callback(WM_MESSAGE*pMsg)
{
   switch(pMsg->MsgId)
  {
   case WM_PAINT:
   if(!b)
   {
  GUI_SetColor(GUI_BLACK);
// GUI_SetBkColor(GUI_BLACK);
  GUI_Clear();
// GUI_SetTextMode(GUI_TEXTMODE_TRANS);
  b=1;
  }
  GUI_SetColor(GUI_GREEN);
  GUI_SetFont(&GUI_FontHZ_MingLiU);
  GUI_DispStringAt("    Cut Speed:2100mm/s",15,20);
  GUI_DispStringAt("FEED SPEED:xxxxmm/min",15,55);
  GUI_DispStringAt("FEED Status:OFF",15,90);
  GUI_DispStringAt("OPERATE Status:STOP",15,125);
  GUI_SetColor(GUI_BLACK);
   break;

   default :WM_DefaultProc(pMsg);
  }

}