Physics2D.BoxCast return incorrect info (5.2.2f1)

Hi there,
I'm writing a custom 2D physic system
what I have a issue is
when I call Physics2D.BoxCast
it return wrong info
as this picture shows
I cast a box to right
and it absolutely should not be 0 angle

I think it's because it is corner
but It should return one of two edge's angle instead(from hit.normal)
this will cause my character go through ground
because it think the right side is flat
since it happen rarely
but that's just not right

my unity version is 5.2.2f1
is new version after this fix it or not?

edit:
I have a concept here
let's say I cast to straight right

the rules should be like this

all judgement base on the cast direction

this can not be done if unity don't fix it
I don't wanna use violence way to make it happen
so please help
really thanks

 

I found why this happen
because in the top picture
it actually contains all situations in second image
then as the result it take the third one

and the key to make this happen is the middle gap line
between 2 edges

Unity should not take that line to collide with
that's must to be ignored because it's even not generate by polygonCollider2D's points

hope someday this can be fix
or the 2D collide system is very unreliable