Comment 9 for bug 1518122

unity8 correctly suspends MonsterWars by calling ubuntu_app_launch_pause_application("monsterwars.t-mon_MonsterWars_0.7")
It doesn't happen as soon as you turn the display off though, as unity8 has to wait until the app has finished initialing first (ie, it has draw its first frame or two). So it happens shortly after the display is turned off.

I can see it worked by running:
$ top -d 0.5 -p $(pidof MonsterWars)

"""
  PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
 3886 phablet 20 0 341140 126028 43480 T 0,0 6,8 0:05.59 MonsterWars
"""

Strangely enough the music keeps playing for 10 seconds or so until if finally goes silent.

In short: qtmir (from unity8 process) is doing its part.