last staff on one instrument has no lines

Rev. 2732 on windows xp.
Create a new score from scratch. Add a the instrument "Violins 1". Click on the right box where it says "Staff 1, Treble clef". Click [Add Below] button four times to get a total of 5 staves. Click [Finish]. On my sm. this results in 5 staves of violins 1 (which I will change to just "Archi") however the bottom one has no lines.