I'm not really sure what the display options Primary, Alternate, Primary (alternate above), Primary (alternate below), Alternate (primary above) and Alternate (primary below) are for. But I think this is a bug:
Start a new sentence diagram.
Make sure Display is set to Primary.
Insert a passage (I used Rom 6:4).
Now choose Display > Primary (alternate below).
Result: the text overlaps the line:

An even worse situation comes up if you do this:
Start a new sentence diagram.
Set display to Alternate.
Insert Passage.
Set display to Primary.
Result: The text is totally garbled:
