I've have quite strange situation here.
https://codesandbox.io/s/7myoj9zp3q
When I want to add new row, I am able to add a new inputs (append to state null values), but I am able to type only one character a time (input looses focus). Am I missing some events or what?
PS - I know that there might be another way around (adding to state ready/almost ready object), but I wanted to get this variant to work.
Fixed by following suggested way read on Mutations Follow Vue's Reactivity Rules https://vuex.vuejs.org/en/mutations.html#mutations-follow-vues-reactivity-rules:
Vue.set(obj, 'newProp', 123)