was simply a pointer to an object on the display list.  At times this object
would disappear from the display list, in the test case because of a concatonation
of two wires, and if you then tried to clone the non-existent object you'd get a 
crash.  This was not merely a bug, but a naive design choice. IMO.
Now the item to repeat is cloned, so will never also be on the display list.