Hi,
It's because the editor and devices behaves differently.
For your editor to fire pause events, you must uncheck "run in background", and then to test it, simply switch from Unity to your Browser or Mail client, then go back to Unity, you will see that the pause event was indeed fired by Unity and PlayMaker.
Check the screencast below to see that it works ( provided you did turn off "run in background")
now, for Android, if that doesn't work, then It's likely more an issue with Unity not forwarding properly or the android device itself.
Let me know how it goes,
Bye,
Jean