Line spacing is not preserved when exporting RTF to HTML and the lines are exported with the default line spacing.

First Footer of a section overrides the First Footer of another section after the merge. After merging 'Parent' document (with a different First Footer which is empty) with 'Child' document (with explicitly set First Footer), the First Footer of 'Child' overrides the First Footer of 'Parent' after PDF export.

Workaround 1: Disable 'Child' document's 'HasDifferentFirstPageHeaderFooter' and clear its First Footer's value:

Telerik.Windows.Documents.Flow.Model.Section section = child.Sections.First();
section.HasDifferentFirstPageHeaderFooter = false;
section.Footers.First.Blocks.Clear();

parent.Sections.First().Footers.Add(HeaderFooterType.First);

When a document has a list in it and the element containing it is cloned into another document, there is a key not found exception if you try to export the second document.

            RadFlowDocument document = new RadFlowDocument();
            if (tableDocument.Sections.First().Blocks.First() is Table workSheetTable)
            {
                Table clonedTable = workSheetTable.Clone(document);
                var newSection = document.Sections.AddSection();
                newSection.Blocks.Add(clonedTable);
            }

            byte[] pdfBytes = pdfProvider.Export(document);
            byte[] docBytes = docxProvider.Export(document);

Nested Mail Merge cannot handle empty lists.

Workaround: Replace the empty list with null.

Merge field group in a single table cell causes it to replicate more times than expected.

Workaround: add a second column to the table and move the TableEnd/GroupEnd/EndGroup/RangeEnd merge field inside it.