Ah, that’a fun one. The root of the problem is this line:
var domElements = getElementsByClassName("HYPE_element", currentSceneElement());
Hype’s runtime is doing a DOM search of elements with the HYPE_element class (likely we use the DOM method for simplicity sake). We expect to know about all items with this class, and have internal data structures in the runtime that map to it. Since you’re cloning a group containing a HYPE_element (and then changing the id which we use as the key on that child), it is failing in the lookup and throwing an error.
A solution would be to remove the HYPE_element class from the child.
So to ruin the “tumult genius of the month” party the general problem is that you shouldn’t manually make elements with the HYPE_element class otherwise the runtime will barf 
.