Positioning of lyrics

[Morten Lemvigh]

I'm setting a vocal piece for SATB. There is an intro with SA and then T 
and B join them in the verse. In the verse, I would like the lyrics to 
be positioned between S and A and between T and B. But when I include 
the intro I cannot get the lyrics to stay between T and B, they jump up 
below A. Here is a minimal example of what I get:
http://www.lemvigh.org/test.png

And here is what I wrote to get it:
http://www.lemvigh.org/test.ly

What should I do in order to get the lyrics to stay between T and B?

Thanks,
Morten