Why Redux.js launches reducer function multiple times on init?

Question

Learning Redux.js and building a demo app.

I have a reducer set like this:

// Imports here
function blocksFunc(state = [], action) {

  switch (action.type) {

  case 'ADD_BLOCK':

    _id++;
    return [...state, {'_class' : 'basic', '_id' : _id }];

  default:

    state = []; 
    return state;
  }
}

const BlockGeneratorReducer = combineReducers({

  blocksFunc,
});

export default BlockGeneratorReducer;

I successfully update the state, but when logging I get the following when page loads:

blocksFunc() type: "@@redux/INIT"

blocksFunc() type: "@@redux/PROBE_UNKNOWN_ACTION_b.f.4.qyoav2.t.9"

blocksFunc() type: "@@redux/INIT"

So blocksFunc function is launched three times with default action.type. On which occasions is the action type "@@redux/INIT" launched? What might "@@redux/PROBE_UNKNOWN_ACTIOM" refer in to?

The full source can be found on git: https://github.com/JaakkoKarhu/redux-react-blockgenerator

The working demo is uploaded to my server: http://jaakkokarhu.com/playground/redux-block-generator/

Since being new with React and Redux, all the other comments regarding the source are also very welcome.

EDIT:

blocksFunc() edited according to DavidWalshes advice.

Answer 1

@@redux/INIT is launched twice on purpose. First time is for testing combineReducers, second one is actual init: https://github.com/reactjs/redux/issues/382

As TenorB pointed out on question comments, @@redux/PROBE_UNKNOWN_ACTION is also launched for testing purpose.

So, after all, these events are not accidentally launched.