left/right page lineup

[karl at aspodata.se]

 How do you line up, in a page spread, the left and right
page text lines ?

I'm trying to make a text booklet (size 115 x 180 mm)
in a dvd-case for a music recording of Buxtehudes
membra Jesu nostri:
 https://en.wikipedia.org/wiki/Membra_Jesu_Nostri

In it I like to have the latin text on the left page
and the translation on the right page. The pages are
too small to have the latin and translation side by side
on the same page.

Now given the files in:
 http://aspodata.se/tmp/tex/
it works fine for the first spread to just have the same amount of
text lines in the tex file. But for the second spread it doesn't work.

Both the latin and the translation have the same amount of lines.
How come it is typeset differently ?
How do I do to solve that without resorting to manually setting
paragraph heights ?

Regards,
/Karl Hammar