bind:this used in {#await} does not trigger reaction

[yoshikiohshima]

Describe the bug
From Stackoverflow [https://stackoverflow.com/questions/58228948/how-do-i-trigger-a-reaction-when-bindthis-is-used-in-await-in-svelte]

<script>
    import TapHere from './TapHere.svelte';
    let enableButton;
    $: enableButtonRect = enableButton && enableButton.getBoundingClientRect();

    let promise = new Promise((resolve) => {
        setInterval(resolve, 3000);
    });
</script>

{#await promise}
<p>
    waiting...
</p>
{:then}
<div>
  <button bind:this={enableButton}>Enable</button>
  <button>Disable</button>
  <TapHere rect={enableButtonRect}/>
</div>
{/await}

The enableButton (and enableButtonRect) should cause TapHere component to react when the promise is resolved. If the div is not enclosed by {#await} it certainly does happen; but {#await} seems to prevent the reaction.

To Reproduce

https://svelte.dev/repl/4e0e477d6a394a83a2d79b3d1fa50525?version=3.12.1
A green "Tap Here!" message should be shown.