Observations get cancelled when updating a tree node.

[mikerobi]

There are scenarios where updating the store will incorrectly cause observations to be canceled.

In this example I do 2 consecutive puts. The first put updates the grid and cancels the observer. The grid has to be refreshed to see the results of the second put. Tested against dojo-1.9.1.

https://gist.github.com/mikerobi/6500909