melismatic left-alignment with \lyricmode

[Monk Panteleimon]

Dear Lilypond users and developers,

I am using 2.8.3 to engrave chant for TTB. I normally use \lyricmode for
such music because it gets the lyric-extenders right regardless of which
voice has the melisma. But now I am noticing that it isn't getting the
left-alignment right. Lyrics are only left-aligned under melismata if there
is a melisma in the topmost voice. Here is my example:

\version "2.8.3"
global = { \set Score.timing = ##f  \key bes \major } 
\score { 
\context ChoirStaff  <<
        \context Staff = top << \clef "G_8"
        \context  Voice = tenone \relative c' { \voiceOne \global  c4 d8([
c]) bes4( a) g a bes2 a g a \fermata  } 
        \context Voice = tentwo \relative c { \voiceTwo \global f4 f f2 f4 f
f( g) g( f) f( ees) d2 \fermata   }
                >>              
        \context Lyrics \lyricmode { In4 that day2 __ all4 his  thoughts2 __
shall __ per -- ish. }
        \context Staff = bottom << \clef "bass" \relative c { \global 
                         { bes4  bes bes2 c4 c d( c) c( bes) c2 d \fermata }
}
                >>
        >>
                
\layout {  \context { \Staff \remove "Time_signature_engraver" \remove
"Bar_number_engraver" }
                \context{ \Lyrics \override LyricSpace #'minimum-distance =
#.8 }
        }               
}


As you can see, the lyrics "that" and "day" are left-ligned (i.e. when
tenor1 has the melisma) but "thoughts shall perish" are not left-aligned.
The last words are instead center-aligned under the first tenor's
half-notes.
Am I doing something wrong? I've not noticed this before. I know that I can
left-align specific lyrics with a \once \override maneuver, but I'd rather
avoid that since it would happen quite often.

Monk Panteleimon