Higher poly count when shadows are on even if no shadow caster present

As the title says, i am having a problem with unity5 (checked it also in unity4 and in that version there is not this problem).

If i create a scene with a single directional light and a few objects i have weird tris/poly counts with shadows.....even with no shadow caster or shadow receivers active, i have a much higher poly count if i leave the "hard shadow" option activated on the light....

Why is that? if there is no one casting or receiving shadows, why the poly count and batches/set pass count increases??

Here are the data:

CASE 1: Light hard shadows ON, shadow casters and receivers ON --> 40k tris, 60k verts, 37 pass calls, 45 batches, 16 shadow casters

CASE 2: light hard shadows ON, shadow casters and receivers OFF -->27k tris, 44k verts, 31 pass call, 34 batches, 0 shadow casters

CASE 3: light hard shadows OFF shadow casters and receivers OFF (or ON doesn't change anything) -->15K tris, 26k verts, 18 pass calls, 20 batches, 0 shadow casters

It is basically DOUBLE the performance to disable the shadows on a light even when there are no shadow casters or receivers....but it makes no sence (and in my case i can't do that because i want to have some model casting shadows and some other not....but simply for keeping the shadows active on the light i more than double the poly count/draw call).

As i said i checked the same scene in unity4 and, there, there is no difference, as it should be, whether i disable all shadows caster/receivers or disable the shadows directly on the light