Fixed. Fascinating bug, thanks for the ping. Since it's Friday afternoon, I'll explain a bit more.
This tile is relatively complex when it comes to it's mover setup, meaning moving parts, in this case all the crashing and falling bits as the level stages progress.
When it comes to more involved setups like in this tile we start using little helper meshes to attach stuff to so we only have to animate one mesh and attach all the other parts to that. Crude but effective. In this scenario one of these helper meshes had a starting position in the middle of play space as you can see here.
Now normally these don't have physics properties and don;t interact with anything in the world at all but this one had a wrong physics type and so still had collision on it. Cool bug.