Scripts which open multiple windows when run in visible mode do not close the windows when the window is supposed to close. 
 
This was a known issue, affecting only SilkPerformer 2011 Hotfix 14.  This issue was addressed in later versions of SilkPerformer.  A short term solution is to use the BrowserCloseWindow function call to close the window like so:

  begin
    BrowserStart(BROWSER_MODE_DEFAULT, 1024, 768);
    BrowserNavigate("demo.borland.com", "Navigate_demo.borland.com (#1)");
    wnd1 := BrowserGetActiveWindow("wnd1");
    ThinkTime(3.6);
    BrowserClick("//A[@textContents='Test Sites']", BUTTON_Left, "Click, A, textContents=Test Sites (#1)");
    BrowserClick("//STRONG[@hideFocus='0']/A[@hideFocus='0']", BUTTON_Left,
      "Click, A, textContents=Internet Compliancy Tests (#1)");
    ThinkTime(3.3);
    BrowserClick("//LI[@hideFocus='0'][3]/A[@hideFocus='0']", BUTTON_Left, "Click, A, textContents=Multiple Windows Tests (#1)");
    BrowserExecuteJavaScript("window.open('http://demo.borland.com/TestSite/multiplewindows/window1.html');");
    wnd2 := BrowserGetActiveWindow("wnd2");
    BrowserCloseWindow(wnd2);
    BrowserActivateWindow(wnd1);
  end TMain;