ARMA 2: Operation Arrowhead BattleEye startup issue & online multiplayer crash. (33930)

Observed: Game refuses to launch normally as BattleEye either fails to start correctly or crashes.

Game complains about invalid registry key yet runs regardless. Game can be run without BattleEye via launch options and graphics/sound are fine in single player campaigns. Able to play, however mouse travels outside of the game window. (I use a triple monitor setup. "Xinerama" disabled in NVIDIA X Server Settings during testing).

Game crashes when trying to access multiplayer online server list.

Steam Play: Proton 3.7-4 Beta

Description: Ubuntu 18.04.1 LTS
Release: 18.04
Codename: bionic
Kernel: 4.18.4-041804-generic #201808220230

Gist: https://gist.github.com/supashang/d096ee4b779570009e25a1076c63a4ed

System Info Gist: https://gist.github.com/supashang/6050de4e5ed8854f58d7152521048170
Intel Core i7 4790K @ 4.3GHz, ASUSTeK COMPUTER INC. Z97-PRO GAMER (SOCKET 1150), Corsair Vengeance Low Profile 16GB Dual-Channel DDR3, 4GB NVIDIA GeForce GTX 970 OC STRIX, Samsung SSD 840 & 850 EVO

Start by reviewing the linked Gist and System Info Gist, then reproduce the BattleEye startup failure and the crash when opening the multiplayer server list with Steam Play Proton 3.7-4 Beta on Ubuntu 18.04. Done means BattleEye starts correctly and the online server list no longer crashes, while the reported registry-key and mouse behavior are understood or separately tracked.