Edits to a block does not update existing instance in the drawing

I created a block from a drawing and later edited the named block.  However, the
changes only apply to the block definition itself and do not update the instances of
the block in the drawing. As a result, I end up with two versions of the same object -
one in the drawing and one as the edited block definition, which is very confusing.

Should changes to a block reflect changes to the drawing?  Or vice versa?