I seem to have this same game freeze. I included my crashdumps (Arma 3-crashdumps.7z). Two of them with mods, one vanilla.

--EDIT-- Or not, my problem might be caused by gfx card / dx11

My game also nags about the need to purchase the Marksmen DLC, but I can still use the new rifles in a quick mission made in editor. I also own the Arma 3 DLC Bundle.

Can confirm. I have also lately used the first person mortar optics, with this handy arty firing solution calculator http://a3arty.arma3.no/ and every fired HE round damages the player.
The damage received from one HE round varies between 0.02 and 0.04.
After firing all HE rounds i had received 0.678469 damage.
Damages both player and the mortar, no difference between 1st person and 3rd person. Happens on flat and uneven surface.

Using the artillery computer no damage sustained.
Vanilla game, no addons.

In fact it does :) I also tested with vehicles too but did not record it. As long as the bush stays intact, you are quite safe. I tried with Marshall's AP rounds and its MG, rounds went through but the guy stood intact.

Can confirm. As long as the soldier is as close to the center of the bush, he is almost invulnerable to gunfire.
Video 1: http://youtu.be/X_M1EqO6Q4E

Video 2: http://youtu.be/2K4wjO-IqpI shows that the rounds penetrate the bush and kill another soldier behind it, but not the guy inside the bush.

Even though i had mods enabled while recording, this also happens in vanilla.

You guys could also include your dxdiag file and crashdumps here like i did, those will help the devs a lot in tracking the problem and fixing it. If you have not done this before, top right corner of this page has a link to a guide for how to do it. (and just in case: http://feedback.arma3.com/how-to-user.html.html ).

For the dxdiag report file: Just type in the Start menu searchbox: "dxdiag" and hit enter, then from the tool "Save all information" -button

Crashdumps, dxdiag and repro mission here: http://www.sendspace.com/filegroup/Cz%2B9Xr7uLa8ppjgaQ1ngSMsEGMreSkqa

Mods: A3
Distribution: 0
Version 0.5.102571
Fault address: 5B166DD7 01:000D5DD7 C:\Pelit\SteamGames\steamapps\common\Arma 3\PhysX3_x86.dll
file: invisible_wall
world: Stratis
Prev. code bytes: 44 D9 04 43 89 5D F4 8B 45 E8 8B 55 E4 8B 4D C0
Fault code bytes: 89 04 8A 8B 17 89 57 04 8B 0E 8B 55 D0 89 4E 04

Registers:
EAX:00000000 EBX:056094F0
ECX:00000000 EDX:642C9610
ESI:17B3004C EDI:055E7C1C
CS:EIP:0023:5B166DD7
SS:ESP:002B:24D2FEA4 EBP:24D2FF38
DS:002B ES:002B FS:0053 GS:002B
Flags:00010246

Short video clip showing the repro: http://www.youtube.com/watch?v=cu7QWG66Pnw