The documentation for the initialize() method of Ui.Drawable indicates that the parameter dictionary will accept keys with the symbol value :x and :y and use them to initialize the drawable object's position. Sadly, the constructor appears to look for :locX and :locY instead.
While this can be worked around easily by calling Ui.Drawable.setLocation(), or by changing the values of the keys in the dictionary passed to the initialize() function.
Travis
