When overriding the HTTP method from post to get on your JsonStore, the method name is case sensitive. It must be capitalized.

var store = new Ext.data.JsonStore({
proxy: new Ext.data.HttpProxy({url: '/data', method: 'GET'})
});

Using method: ‘get’ does not work - it will still be an http post. This is clearly stated in the docs, but it’s too bad it’s case-sensitive.