Reply to mute and shan...
The first who "observed" a problem with hit detection where NTKB and me, along with other who I don't remember (a quick guess would be UN17, taque, duke, perhaps another GD and some DbD... but that's uninportant) when we beta tested the BS4 muty early on, on GD training/testing server.
=== test and results decription ===
The test was having one player being a building, prone and leaning out of the side (it was leaning on the left side to be more precise).
While the prone player was aiming (I'm not sure if it happen also when "hipped" because that quite a while since we have done those tests), another, about 25 meters away, shot at him.
The conclusion was that a part of the left arm was not covered by the hitdetection system. The test has not been done for the right side so no conclusions can be drawn for that side. By no mean have we concluded that the player cannot be hit while prone leaning. The conclusion was that a small part of the player (the arm) cannot be hit while prone leaning on the left side. This is particularly important in a situation like the one we tested, where most of the player is occulted by a structure.
I have layed down two hypothesis following those conclusions. The first and the more obvious one, which is the one every one takes for granted, is that BS4 is bugged and that it's multi-cylinder hit detection does not cover the arm. The second hypothesis I have suggested, is that the original Infiltration hit detection for prone leaning does not cover that region of the player. Hence, since BS4 is a post processing of an impact of the original hitbox from Infiltration, the detection cannot be made.
That being said, I have yet to verify the second hypothesis. In order to do that, I suggest the following simple test. Redo the test I have previously described with BS4 running. With this test establish clearly the "bugged" position and deficient impact zone (identified with screenshots). Then, turn BS4 off to go to the normal hit detection, and tryout the exact same position. If the same problem happens, it's a problem with the original hit detection and it means that INF 2.9 was bugged from day one.
=== My personal conclusion ===
I think people are overeacting a lot about this problem. Most of the body is still pretty much hittable, even when prone leaning. Some people clearly used this problem as an excuse for not being able to hit prone people. Of course it's harder to hit a prone player. As Tiffy said in another thread, when shot at, you don't start jumping around like a crazy bunny... you hit the ground. Why? because it's harder to shoot at someone prone.
This whole bugged prone things has been why over-hyped. Now people start accusing other of prone leaning like it was some sort of dirty hack or aimbot. Most of those who makes the most noise about this don't even know what the problem is and how important it is.
As i told yurch a while back on the test server, this problem needs to be on the "has to be fixed" list, but is not critical. That is still my opinion today.