V-model and 2D arrays not working

Hi everyone,
I am new to HTML/JS/Vue and I am stuck at a point which is driving me crazy. The question is fairly simple: Why does the code below not work? In particular, the browser tells me, that testData[0][0] is not a “valid JavaScript member expression” for the input element. I am pretty sure it is :wink: The output with {{}} works perfectly fine and shows a “1”. Why is the input not working as expected? If I reduce the number of dimensions in the array to one, it also works perfectly fine.
Any help is welcome :slight_smile:

<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
  <title>Test</title>
  <script src="https://unpkg.com/vue@next"></script>
</head>
<body>
    <div id="app"></div>

    <script>
        const app = Vue.createApp({
            template:
            `<div>
                <div>{{testData[0][0]}}</div>
                <div><input v-model="testData[0][0]"></div>
            </div>`,
            data() {
                return {
                    testData: [["1", "2"], ["3", "4"]]
                }
            }
        })

        const mountedApp = app.mount('#app')
    </script>
</body>
</html>

OK, I was able to figure out that this was caused by the release that came out ~24 hours ago. It seems that this issue was introduced in v3.1.0-beta.6, because v3.1.0-beta.5 works just fine. Also v3.0.11 is working.
Is this a bug or a feature?

Seems to be a bug. I (re)opened an issue: v-model value must be a valid JavaScript member expression · Issue #3910 · vuejs/vue-next · GitHub