How tall is the field? Is it only one line of text tall? If so, during editing the field pops out to show more of the contents, but only one line of text will be visible when printing/Previewing/PDF'ing. You'd need to resize the field to make it more than one line tall. There's a sliding option you can specify in the Inspector for a selected layout object such as your field that can be used to "shrink" the field down when the space for two or more lines of text aren't needed to display the full contents of the field.