I keep trying to play around with this to identify what's happening more
clearly, but it seems like the lyrics when it's in polyphony are somehow
not "resetting" once it goes back to one voice. If I omit all lyrics, then
the voices lay out correctly. The strange thing is that I use the pattern
elsewhere in the score without issues, so maybe there's also some factor
specific to the voices as well.
this problem (about dying contexts) is fixed in 2.19.83.
Thus I'd switch to this version.
In general I'd recommend not to created a whole bunch of new contexts
(even of different kind: Voices and Lyrics) while being in another
LilyPond may not be able to sort out what you intend.
Better initiate what you need right from the start (probably keeping
them alive) and distribute content as you like.