SharePoint 2010 pages throw JavaScript error "SP.Ribbon.PageState is null" when we try to connect 2 web parts on a publishing page

What?

SharePoint 2010 pages throw JavaScript error "SP.Ribbon.PageState is null" when we try to connect 2 web parts on a publishing page

Why?

Don't know :) but I know a fix

How?

Adding the "Page Content" field to the page layout (add it to the content type that the page layout is tagged to) has fixed the issue.

1. <PublishingWebControls:RichHtmlField id="PageContent" FieldName="PublishingPageContent" runat="server">  
2. </PublishingWebControls:RichHtmlField>