When rendering lists, ensure that form fields don't copy value of previous node

[rglover]

Weird one. If I have a form input that's rendered inside of a list, when that list changes, the node that used to be in the position of the current list item has it's value still present in the input (e.g., if I had a select with "Pizza" in the old node and "Apple" in the current, "Pizza" still remains). The render doesn't break, but it's confusing if you don't realize what's happening.