Create an excluded block 8 mm high, create a sketch on the face, creating a 6 mm high square, then extruded this through the block. Now increase the height of a block to 10 mm, then back to the sketch of the face and increase the height of the square, to 9 mm This excludes the whole height of the block of 10 mm rather than than 9 mm from the updated sketch ?
One would assume that the extruded square would take the dimensions of the sketch.