I'm sorry this was marked fixed. That was unintentional.
The problem is that the automatically generated id's are strings like 'ext-record-1'. For consistency, this id is just like any other id until it is changed by the server or client side, and thus needs the id field to be type auto.
Maybe I can add a configuration on the identifier that indicates the type the id's it produces are. This way you could make a purely sequential integer identifier (Ext.data.identifier.Sequential) which would keep the field as type 'int'.
We are also still discussing internally how we can keep the identifier's seed in sync with the local storage database.