Invalid .d.ts file generated only in watch mode

[lwalden]

Given the following:

<script lang="ts">
    //imports here

    interface ICustomer {
        expanded: boolean
        item: ICustomerResponse
    }

    @Component
    export default class Customers extends Vue {
        selectedCustomer: ICustomer | null = null;
    }
</script>

When I run vuetype this generates an error:
Emit Failed: - example.vue.d.ts
Error: [17,23] Public property 'selectedCustomer' of exported class has or is using private name 'ICustomer'.

But when I run vuetype --watch against the same .vue file a d.ts file is emited. The reference to ICustomer is not imported or referenced so the Typescript compiler complains.

I would expect watch mode to emit the same error as running vuetype once.