RadRichTextBox/RadDocumentEditor's MailMerge(bool) method doesn't respect the startEachRecordOnNewPage parameter. When the parameter is set to 'false', records are still merged on different pages, instead of on one.

Workaround: Use RadDocumentMerger to append the resultant documents:
http://docs.telerik.com/devtools/wpf/controls/radrichtextbox/features/merge-documents/append