In the second aliyah of Bamidbar (B'midbar? Bemidbar? 
) -- the word "sheimos" is spelled with a vav, malei, until 1:26, then it's chaser, and for the rest of the sh'vatim (except Menashe) is chaser.
What's that about? Any insights?
-- Sholom
I don't mean to be snarky
But I would start with a Concordance and see if there is any pattern to the variations of the spelling of this word.