Yep... odd combination of React's 'diff' mechanism and <Datepicker> not accounting for the occasion where an incoming value is actually blank. Fixed as .

Further investigation shows this is likely related to the Datepicker component as unshift works just fine when using a TextField field instead of a Datepicker field. I'll follow up with for assistance debugging.

Then, sorry, I am out of ideas. (I don't know redux-form.)

Maybe file an issue on the package?

Agreed, it looks that way, but the code is onClick={() => fields.push({})}, i.e. it's already pushing on an empty object per the example at https://redux-form.com/7.1.2/examples/fieldarrays/,

The documentation for FieldArray.push(value: Any) doesn't really tell you what's going on or how the argument is used:

Adds a value to the end of the array. Returns nothing. This is not a mutator; it dispatches an action which updates the state in Redux, which will cause your component to rerender.

I tried using a full-fledged dummy object, e.g.

but the results were the same.

Without looking at the code, this sounds like a reference-aliasing problem. Try making a shallow copy with newObject = Object.assign({}, originalObject) and see if that fixes it.