Value inside v-slot in a v-for won't update

[jedrula]

Version

2.6.0

Reproduction link

https://github.com/jedrula/slot-updates-on-vue-2.6
jsfiddle: http://jsfiddle.net/sj8wcx0k/

Steps to reproduce

You can see the problem on a deployed version of https://github.com/jedrula/slot-updates-on-vue-2.6 here: http://slot-updates-vue-26.surge.sh/

You run into a problem like that if

1. you have a v-slot inside a v-for and in that v-slot you render an item from v-for
2. you update whole array that drives the v-for

What is expected?

Rendered item in v-for should behave in a same way as rendered item in v-for inside a v-slot - it should be re-rendered when the whole array driving the v-for changes.

I'd expect no changes in behavior from Vue 2.5.22. You can see how it behaves on the same code with vue 2.5.22. I have deployed same code with downgraded Vue version here: http://slot-updates-vue-25.surge.sh/

What is actually happening?

The item inside v-for in a v-slot is not re-rendered:
https://github.com/jedrula/slot-updates-on-vue-2.6/blob/master/src/App.vue#L6

---

I know that the issue can be resolved by providing proper v-key to the v-for. The confusing part though is that the even without the v-key this line is updated: https://github.com/jedrula/slot-updates-on-vue-2.6/blob/master/src/App.vue#L4 but this line is not: https://github.com/jedrula/slot-updates-on-vue-2.6/blob/master/src/App.vue#L6.

If that's not a bug but something I don't understand about scoped slots it might be good to add some information about that in some Vue reactivity gotchas ? I wonder why it bit me given a change from 2.5 -> 2.6 should not be breaking.