Victor Evangelista16,745 Points
Here is my solution: https://w.trhou.se/m63kdejjz3
I am working with most of the original code. I've added two new functions:
Whenever the user adds a new list item, the button will flicker for a quick moment before its replaced by a button without the disabled styling.
Steven Parker163,760 Points
To avoid "flashing", make sure that the buttons are all in the desired state before the new list item is added to the DOM. Otherwise, there will always be a moment between when the list item is added and the states are reset where the default appearance might be seen.