As mordekaiser's ult ends, any damage that is supposed to happen at the same time the ult turns off just doesnt go through. Happened with Morde Q, started the animation while in the ult zone, it turned off as the Q hits the ground, and the enemy didnt take damage from it. Same thing happened in the next game, but with a tower shot that just didnt deal any damage.
You can't do Damage between realms, They're two different areas so the damage will travel between but there are some Spells that will Work if you use Ziggs W in the Original Realm and Mordekasier ults you, it will still work and knockback away from him. You have to watch some of the YT Videos to get hang of the skills that you can use between realms
People can also run out of your ult
I don't think this is a bug. This was something noticed early in the PBE. Things that happen in one realm stay in that realm.
