When 'Run In Background' is disabled for Linux standalone builds, they still keep on running in the background.

Steps to reproduce:
1) Open the attached project.
2) Build for Linux.
3) Run the build in Windowed Mode.
4) When the build launches, click outside of the player window.

Notice that particle system is still active in the player. A short stutter (around 1s) occurs in the player, player view is not updated during that period, but resumes afterwards.
This does not occur on macOS and Windows.

Reproduced on:
2017.1.0a4 (trunk), 5.6.0b10, 5.5.2f1