That seems like a remarkably strange definition of a primary key. Are all of those columns really identification of an object, and not properties of the object?
In any case, I'll bet a lot of money that your can't-update problem is related to the fuzzy behavior of floating-point columns. Just because a float8 value prints out as "1.2345" doesn't mean that it'll be considered equal to a value you write as "1.2345". If this fact astonishes you, you should likely switch to type numeric.
regards, tom lane
Dear Tom, you can bet all your money because you are right.
I drop the table and re-created using numeric instead double precision.
Now everything is ok, I can update every row of the table.