Uncaught TypeError: Cannot read property 'scrollTop' of null

[xiaix]

So, in Eureka, this code works fine:

function close_and_reopen_UI_Page()
{
       // Close this current pop-up UI page
       GlideDialogWindow.get().destroy();
       // Re-open this UI pop-up page again, but now showing updated info
       var dialog = new GlideDialogWindow('bcp_BCC_Author_EDIT');
       dialog.render();
}

However, in Geneva, when it hits line 8, dialog.render(), my web browser stays in a permanent .5 opacity mode and looking in console log, I see:

Which upon inspection shows:

[xiaix]

Well, I found out how to fix the issue, but I can't figure out why it has to be done this way:

var UI_reload_Timer = 0;

function reopenUI()
{
       clearInterval(UI_reload_Timer);

       var dialog = new GlideDialogWindow('bcp_BCC_Author_EDIT');
       dialog.render();
}

function close_and_reopen_UI_Page()
{
       UI_reload_Timer = setInterval(function(){ reopenUI(); }, 500);

       // Close this current pop-up UI page
       GlideDialogWindow.get().destroy();

       // Re-open this UI pop-up page again, but now showing updated info
       var dialog = new GlideDialogWindow('bcp_BCC_Author_EDIT');
       dialog.render();
}

Why do I need to set a delay to re-open the dialog window?