Array splicing and dom-repeat lead to wrong path in deep property observers

[Simona Butnaru]

When adding an element in array, using splice method, and then change a subproperty from the added item, the path from array observation is not the correct one. 
Let's say we have a persons array with 11 objects, each object having name and age as properties. When adding a person {name: Sim, age: 24} on position 2, and after change the property name of person Sim, the observer method returns the path "data.#11.name".
I expected the path to be "data.#2.name" because I added the item on the second position.

Here is a jsfiddle that reproduces the error. https://jsfiddle.net/simona_butnaru/zfwewthr/5/

I made a little research and I've seen that the issue is from polymer, at the add function from Polymer.Collection. This line (var key = this.store.push(item) - 1;) sets the key to be the length of array, and I think the key shoud be the position where the item was added in array.

[Rob Dodson]

Created an issue for this: https://github.com/Polymer/polymer/issues/3316

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[Kayce Basques]

I think I documented this recently, but the update is not live yet...

I think what you're seeing is intended behavior, see:

https://github.com/Polymer/docs/pull/1457/files#diff-07936cc3163b32c7b2a4f859ae877754R550