I have the tinymce -control as a WYSIWYG-Editior in my asp.net page.
When I have e.g. a Text in Bold, after the Postback it is shown as
\"
You can use this code for solving your problem:
TextAreaID.Text = Server.HtmlDecode("hello");
hello
I found it in this post : https://stackoverflow.com/a/8029637/1509986
If you get some security errors you can use
validateRequest="false"
in your page.