The functionality exists to dynamically add a new row but this only fires if you tab to the checkbox or replacement word field and make a change in that field.
If you tab out of the keyword to replace box and do nothing but tab along then no new row is added, this is not ideal behavior - especially when adding a very long list such as I have.
I suggest a new row should be appended as soon as the keyword to replace box has content and loses focus.
I assume this is a bug. Can anyone else reproduce this in other browsers or is it just a chrome issue?