If the cursor is confined in Linux standalone builds, system menus (like Dash on Ubuntu) remain on top of the app, even when the app window is clicked on.

Steps to reproduce:
1) Open the latest attached project.
2) Build the project as a Linux Standalone player.
3) Run the build.
4) Check 'Confine Cursor' checkbox.
5) Press a system key that brings up a system menu (Alt or Super).
- Dash should show up.
6) Press inside the player window.

The system menu does not go to the background and stays on top of the player. If the cursor is not confined, the menus go behind the player.

Reproduced on:
5.5.0xb5, 5.4.1f1