left edge of lyrics alignment inconsistent

[Todd M . Lewis]

I'm not sure whether this is a bug, but I have not found a way around it yet.

The TeX file at http://tarna.oit.unc.edu/~utoddl/lilypond/ produces music with 4
verses of text, each broken into 4 systems. The first word of each line of text
in the first three systems is centered on the associated note. However, the last
system begins with lyrics left aligned to the associated note. (I've also put
the PostScript output there so you can see what I'm talking about.)

Is this a bug? Why is it happening? How can I control whether the first word of
lyrics in each system is left aligned vs. centered with respect to its
associated note? (I like the left aligned look, but I'd settle for either. Both
is bizarre.)

I'm using Lilypond 2.7.18 (as indicated on the "\version" line) on Linux.  I
would have made a smaller example, but I'm still a little unsure of how all the
pieces fit together and interact with each other, and I didn't want to remove
something that may be important.