When I edit a lyric and move the cursor left or right there is a difference between the selected lyric (below staff and orange) and the box where I can edit lyrics.
Just as when you’re in note input, the caret where the next note will appear is one position ahead of the selected note (i.e. the last note you input is selected, even as you are about to input the next one), when you’re in lyric input, the last input lyric is selected while the popover at the next position is open. So it might seem a bit weird but it’s actually quite logical and consistent with how other input methods within the application work.