How to prevent blur from adding input in v-combobox

In Vuetify.js, when using <v-combobox> when I click away, the value I had typed is added to the model.

How can I prevent this?

https://vuetifyjs.com/en/components/combobox

https://codepen.io/anon/pen/NVQBWz?&editable=true&editors=101

What's strange is that the JSFiddle in the example site works, but if I copy the HTML/JS exactly into my app I experience this.

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