Steps to reproduce:
1) Open the attached project or create a new one.
2) Build for Linux on a Windows or OSX machine.
3) Run the build on a Linux machine.
4) Try to close the build using 'X'.

The build doesn't close. It can only be closed using the System Monitor tool or via the Terminal. Two instances of the build open at the same time. Running the build with the -force-opengl command-line argument makes the issue disappear.

Reproduced on:
5.4.0b25, 5.4.0b23, 5.4.0b22 - build didn't open at all.

Did not reproduce:
5.5.0a3, 5.3.5p7, 5.2.4f1

Building with the latest version available for Linux - 5.4.0b23 works as expected.