Business tour fullscreen mode bug

Issue transferred from https://github.com/ValveSoftware/Proton/issues/752.
@jakubreron posted on 2018-08-27T12:17:55:

Fullscreen mode in Business Tour has a bug.
When you try to alt tab in fullscreen mode and then go back, the screen is black and game is a small square in the top left corner.

The device is: ThinkPad x240
STEAM SYSTEM INFO
Computer Information:
Manufacturer: Unknown
Model: Unknown
Form Factor: Laptop
No Touch Input Detected

Processor Information:
CPU Vendor: GenuineIntel
CPU Brand: Intel(R) Core(TM) i5-4300U CPU @ 1.90GHz
CPU Family: 0x6
CPU Model: 0x45
CPU Stepping: 0x1
CPU Type: 0x0
Speed: 2900 Mhz
4 logical processors
2 physical processors
HyperThreading: Supported
FCMOV: Supported
SSE2: Supported
SSE3: Supported
SSSE3: Supported
SSE4a: Unsupported
SSE41: Supported
SSE42: Supported
AES: Supported
AVX: Supported
CMPXCHG16B: Supported
LAHF/SAHF: Supported
PrefetchW: Unsupported

Operating System Version:
elementary OS 0.4.1 Loki (64 bit)
Kernel Name: Linux
Kernel Version: 4.15.0-33-generic
X Server Vendor: The X.Org Foundation
X Server Release: 11906000
X Window Manager: Mutter(Gala)
Steam Runtime Version: steam-runtime-beta-release_2018-06-14

Video Card:
Driver: Intel Open Source Technology Center Mesa DRI Intel(R) Haswell Mobile x86/MMX/SSE2
Driver Version: 3.0 Mesa 18.0.5
OpenGL Version: 3.0
Desktop Color Depth: 24 bits per pixel
Monitor Refresh Rate: 60 Hz
VendorID: 0x8086
DeviceID: 0xa16
Revision Not Detected
Number of Monitors: 1
Number of Logical Video Cards: 1
Primary Display Resolution: 1366 x 768
Desktop Resolution: 1366 x 768
Primary Display Size: 10.91" x 6.14" (12.48" diag)
27.7cm x 15.6cm (31.7cm diag)
Primary VRAM Not Detected

Sound card:
Audio device: Intel Haswell HDMI

Memory:
RAM: 7668 Mb

Miscellaneous:
UI Language: English
LANG: en_GB.UTF-8
Total Hard Disk Space Available: 112546 Mb
Largest Free Hard Disk Block: 73338 Mb
VR Headset: None detected