New slot syntax doesn't work the same way as old syntax (in some cases)

[hivokas]

Version

2.6.14

Reproduction link

https://github.com/hivokas/vue-2-slots-issue

Steps to reproduce

1. Clone the repo
2. Run npm run serve
3. Change the value in the text input

What is expected?

Preview updates with both old and new slot syntax (here: https://github.com/hivokas/vue-2-slots-issue/blob/cd7f3a6db790472b88421a1497ae14d4135d23ef/src/components/PublishToSocialStep.vue#L4).

What is actually happening?

Preview updates with old slot syntax, but doesn't update with new slot syntax.

Video demonstration of the problem:

https://user-images.githubusercontent.com/22997803/130232152-bd5e445d-600e-4816-b140-685d1fd6c3a8.mp4

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I've updated the old deprecated slot syntax to the new one.