Copying objects with formatted text loses the formatting. This is because while the text format property is retained for the object itself, the text cell formatting does not survive the copy and paste operation. I cannot tell if the problem occurs during the copy or the paste.
This can be tested by simply (at run time) dropping a text block onto the diagram, F2 then type some text, then format the text with bold and italic. Then copy the object and paste onto the same diagram. Note that the text is no-longer bold, nor italicised.