relative mode occasionally gets forgotten?

[Chip]

I've come across this a couple times - when I am inputting a song it all 
works fine in \relative mode. I do some editing, some copy/paste from 
one part to another, view the resulting pdf and see the octaves are all 
messed up. The only way to fix them is to use absolute octave marks in 
small sections, usually only a few measures, to get the song to print 
correctly. Then for whatever reason, after those few measures the rest 
of the song is just fine. This seems to be completely random, has 
happened in a couple different songs, in different versions of lilypond.
Has anyone seen this kind of behavior? Just seems rather odd.
--
Chip