I am using month and year format inside an field array with redux form where I ma repeating same month field on a click of a button and also deleting the filed while clicking on delete button.

### I'm Submitting a ...

```
[ x] Bug report
[ ] Feature request
[ x] Support request
```

### Steps to Reproduce
I am using month and year format inside an field array with redux form where I am repeating same month field on a click of a button and also deleting the filed while clicking on delete button. When I am using defaultValue prop Then I after deleting fiels (say I have 4 field array fields then when I delete the 4th one with month and year field the remaining should show their own value but unfortunately I am getting the value of 4th field in 3rd field date.)

### Expected Results
Changed month field value

### Actual Results
Same field value for month picker if I delete previoue result

The report names react-datetime, React, redux-form, month/year formatting, field arrays, and defaultValue, but provides no version, source file, test, or runnable example. Start by reproducing the field-array deletion behavior and checking how the month/year picker handles defaultValue; done means remaining fields retain their own values after deletion.

Written by the indexing model from the issue text.