Sharepoint 2013, web part, rich text boxes

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I am developing a SharePoint 2013 web part as a maintenance interface to a SharePoint 2013 list using C# in Visual Studio 2015 with the .Net 4.5 framework. The list fields include single line text, multi-line text, date fields, selection dropdowns and selection checkbox fields. All the multi-line text boxes are defined as Rich text (Bold, italics, text alignment, hyperlinks).
The ascx page for the web part defines these multi-line text boxes as <SP:InputFormTextBox ID="rtb1" runat="server" TextMode="MultiLine" Rows="10" RichText="true" RichTextMode="Compatible" Style="width:100%;"> This definition causes a text box header for character type, emphasis, direction and color selection. Bold, italics, underline, and direction work. The others (color, font, etc. don’t work).
I am able to define and insert rows into the SharePoint List from this page using the formatting available from the rich text selections that work.
On retrieval of an individual row from the list to the controls shown on the page, all the controls load correctly except the rich text boxes (SP:InputFormTextBox). In IE11 the fields are empty, in Edge a typical rich text field will show as { } with its HTML editing but without the formatting header strip.

What I have tried:

Various sites have recommended removing the div tag, leaving the HTML editing { CCCccc } but that doesn’t show in IE11 either.
I currently have the master page with the tag “<meta http-equiv="X-UA-Compatible" content="IE=edge"/>” just under the tag. Using IE=10 or IE=11 doesn’t work any better.
In summary, the rich text boxes don’t load from the list and appear empty: clicking on them shows the cursor at the first position.
Extensive internet search shows a lot of solutions for SharePoint 2003, 2007, and 2010 with little for 2013 and nothing that works. Perhaps a non-SharePoint rich text box is in order although there is none in the 4.5 framework. I am constrained in using JavaScript solutions or COTS that are not Open Source.
Can anyone propose a solution that works? Thanks.