To recap you problem: When there is no write-in text and the Ballot Options flag is for write-in text below the line then the line for the last write-in candidate is drawn on top of the race box line.
There are two work arounds.
1) Is the one you have found. that is place a blank line - all it needs to be is a single space character.
2) Set the Ballot Options flag to write-in text above the line.
We could enhance GEMS by limiting the write-in line to be 1/32 inch above the bottom of the "candidate box".