core-list of custom elements contains invalid data after scrolling down the list.

[dough10]

i am getting some strange data returns from my core-list of custom elements. i describe the issue in more detail in a stackoverflow post here. http://stackoverflow.com/questions/28533949/core-list-of-custom-elements-that-use-input-data-to-get-more-json-is-holding-old.

[denevell]

Are you using a auto-binding template? If so, then try putting in an {{index}} in core-list's template. Might be related to #78.