When "End" is used to bring an actor to the closest surface below it, if that surface is another actor that is set to simulate physics the first actor will go inside the actor simulating physics rather than come to rest on top of it.
Edit MattK: What seems to be happening is that the process of setting the simulate physics flag on an object (static mesh for example) breaks the line check that happens when "end" is hit from working. Even if you disable simulate physics afterwards it will never work again.
Head over to the existing Questions & Answers thread and let us know what's up.