lyric extender not so good

[Yuji IMAI 今井雄治]

Hi, users.
I found a trouble about lyric extender,
version 2.13.23 through 2.13.26
Only extender on a system, too narrow space in two lyrics
as following code:

---
\version "2.13.26"
\include "english.ly"

vocal = \relative {
  c4 d e f
  c4 d e f
  c4 d e f~ \break
  f4 r r2
  R1
  R1
}

text = \lyricmode {
  do re mi fa
  do re mi fa
  do re mi fa __
}

\score {
  <<
    \new Staff { \vocal }
    \addlyrics { \text }
    \addlyrics { \text }
  >>
}
---

thanks for reading.

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Yuji IMAI  今井雄治