Extension lines in lyrics

When writing lyrics to a song, there is often a word, which extends over several notes. This is usually indicated by a straight line, following the respective word.
For this purpose, I have tried to highlight the starting note, and add a straight "hold" line from the "Lines" palette. In the start, the line is always too long and in the wrong position. So I adjust its length, and - after de-activating "automatic position" - drag it into the right position. This procedure is a bit awkward, but it works.
The problem is, however, that after saving and closing, the lines are right back in their original length and position, when I re-open the file.
Obviously, I am not using the right method. Can any one help, please?