Broken input in case of conditions in array

### Are you submitting a **bug report** or a **feature request**?
bug
### What is the current behavior?
https://www.loom.com/share/a453878abb5147e18acb0080cee6f010

### What is the expected behavior?
Input will work properly and exception won't be thrown
### Sandbox Link

https://codesandbox.io/s/react-final-form-field-arrays-20edb
https://codesandbox.io/s/react-final-form-field-arrays-cxzi7
### What's your environment?
see sandbox

### Other information

Reproduce
1) add two items to array
2) type "a" to input in the first row
3) type "b" to input in the second input
4) click "remove customer"
5) try to type to input Test Name2 and see console errors
watch video for more detailed information