The font, the text color, the style all get pasted unless you specifically select the option to paste unformatted text.
This auto-enter calculation will automatically strip all text formatting info from the text in the field so that formats specified for the field object on the layout can format the text:
TextFormatRemove ( Self )
and clear the "do not replace exsting value..." check box.
Please note that this also prevents a user from selecting text in this field and selecting text formats from the formatting tool bar.