Wildcat - I was having the same problem. Thanks for logging it so On-Core can address it in future updates.
In the meantime, there is a workaround. Just add multiple spaces at the end of the first line of text until the second line of text gets 'knocked over' to the next line. How many spaces should you put in? You will need to use trial and error to get it right, previewing the invoice to see whether you have the right number of spaces, or too few.
It's a little clunky, but it does work.
Feel free to contact me if my instructions aren't clear.
Cheers,
Paul.