Extending a melisma on two notes makes the melisma colide with previous lyrics

451404f6e0 on Windows

1. Create a score for flute and ass 4 quarter notes
2. Select the first note, Ctrl + L and add some letters to have some lyric under the first note
3. Press underscore once
4. Press underscore a second time

Expected result: a melisma covering the 2nd and 3rd quarter note
Actual result: the melisma is under the word we entered in 2.