During K'rias Hamegillah, I thought I heard the Ba'al K'riah say "Balaila hu" instead of "Balaila hahu". [The person whose job it is to correct insists otherwise] I decided not to reread that word in my Megillah for two reasons.
Number One: There is really no difference in meaning. The Radak writes in Michlol (pg 42) that a "heh hayediah" modifying a noun and an adjective (2 words read together) can be placed on the first , second or both words. [hence the machlokes Rav Shabsai Sofer and Matteh Moshe about "bizman haze"vs. "baz'man haze"] So grammatically "balaila hu" means the same thing as "balaila hahu." [The "beis" includes within it a "heh hayediah," hence the patach, and dagesh chazak in the lamed]
Number Two: There are 4 places in Tanach where "balaila hahu" is written "balaila hu". [B'reishis 19:33, 30:16, 32:23;Shmuel I 19:10] so even if there was a change in meaning, one might argue that where exceptions to the rule exist, one need not correct the mistake, as its correct meaning is still within the realm of possibe interpretation.