regression with :class and v-bind

[cexbrayat]

Version

3.2.0-beta.2

Reproduction link

SFC Playground

Steps to reproduce

As you can see in the SFC playground:

<template>
  <button :class="{ btn: true }">1</button>
  <button v-bind="{ disabled: true }" :class="{ btn: true }">2</button>
  <button :class="{ btn: true }" v-bind="{ disabled: true }">3</button>
</template>

<style>
  .btn {
    color: red;
  }
</style>

What is expected?

The first and second button do have the class btn applied.

What is actually happening?

The last one, with v-bind after :class has a class [object Object].

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This was spotted by @logaretm when I reported an issue that I believed to be in vee-validate, but it turns out to be a regression in vue-next. Downgrading to v3.1.3 makes it work again.