Hi again!
Solved the mistery 
It was very logical but sometimes mind does not work as it should…the problem was created by some of the fields of the table being of type char. When populating the table with INSERT OVERWRITE, for all fields of type char(50), even if the values were less then 50, it will automatically add empty characters to fill the whole space reserved for the char data type. And this is actually the main difference between char and varchar. The later will occupy a variable amount of space based on the value stored. But still don’t understand why this does not happen when using LOAD