Yes, I can see that here too. For now, you could copy the phrase to somewhere where there’s nothing else after it (maybe a new flow or the last couple of bars in the flow, input the lyric, get the correct extension, then paste it back into place. (You could also temporarily delete everything afterwards and re-input the lyric with extension but that’s probably not the safest route!)
Edit: or even easier, select the existing lyric with not-long-enough extender line and press Shift-Alt-Right arrow to lengthen it to the last note in the phrase before the multi-bar rest.