I guess she(?) expected the dotted borders not be drawn above the image, but to be limited by the floating picture.
I'm not sure that would be the correct behaviour. Floats affect the contents of other elements, but the borders? What the block with a border is higher, should only the top border be reduced? What should happen with the right border if present? One could use the z-index property to ensure the image appears on top of the border, but z-index is not in the ePub spec.