One more for lyric extenders

I'm still on version 3.6.2 and I'm wondering why, after following the directions, I get extenders that sometimes look like this (see attachment). After typing the word "right", I pressed shift underscore once. It produced a very short extender. If I tried doing the same thing but pressing the underscore key twice, it disappeared entirely. It would be a lot easier to see if the line extended by a reasonable distance. Is there a way to do this without resorting to awkward workarounds?

Thanks.