Lyric-notehead alignment problem

[Illtud Daniel]

[apologies - I originally sent this to lilypond-bugs, I shouldn't
have]

I'm getting lyrics left-aligned to noteheads  with autobeaming off.
I'm looking for normal alignment (first vowel of syllable).
See the attached .png - it seems to be left-aligning every syllable
except for the last syllable on a beam.

This is a stripped down snippet that compiles and illustrates
the problem I've got:

\version "2.10.13"

\score  {

<<
\new Voice = "alaw"
\relative c''
 {
        \time 2/4
        \key g \minor
        \clef treble

        \autoBeamOff

        bes8[ d d c] |
        bes[ d ees d16 d] |

        \bar "||"
}

\new Lyrics \lyricmode {

        Ar8 ddydd Sul aeth
        Dic yn ben -- noeth16 mewn

} >>
}


Is this a bug, or my problem? Can I fix it? Am I doing
something totally wrong (I'm a lilypond starter). I
realise that my notation is unusual (my beaming doesn't
indicate melismas), but I'm copying an 18th century
original, and it needs to stay that way.

Also, with languages with a different vowel set (this is
Welsh!) is there a way I can tell lilypond about these
so that the 'first vowel notehead alignment' works properly
with 'aeouiwy' - the Welsh vowel set?

Thanks.

--
Illtud Daniel                                 address@hidden