I have a new project using version 4.9.0 for the first time.  I'm getting an error when I try and insert a Razor macro into the Richtext Editor.  The error appears in the "Click to Add Macro" popup window when I click the OK button. 

This is a very simple macro and a very simple content page.  There is a pageName property on the page but there is nothing special about it.  Something I've done a zillion times, but probably the first time iIve inserted a macro in the RTE using 4.9.0.  Is this a known bug?

Server Error in '/' Application.
Item has already been added. Key in dictionary: 'pageName'  Key being added: 'pageName'Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. 

Exception Details: System.ArgumentException: Item has already been added. Key in dictionary: 'pageName'  Key being added: 'pageName'

Source Error: 

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace: 

[ArgumentException: Item has already been added. Key in dictionary: 'pageName'  Key being added: 'pageName']
   System.Collections.Hashtable.Insert(Object key, Object nvalue, Boolean add) +12643638
   umbraco.page..ctor(Int32 Id, Guid Version) +616
   umbraco.presentation.tinymce3.insertMacro.renderMacro_Click(Object sender, EventArgs e) +1142
   umbraco.presentation.tinymce3.insertMacro.Page_Load(Object sender, EventArgs e) +907
   System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object o, Object t, EventArgs e) +25
   System.EventHandler.Invoke(Object sender, EventArgs e) +0
   umbraco.BasePages.BasePage.OnLoad(EventArgs e) +19
   System.Web.UI.Control.LoadRecursive() +71
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +3064








Version Information: Microsoft .NET Framework Version:4.0.30319; ASP.NET Version:4.0.30319.1