Hidden embedded toot becomes very tall

[BenLubar]

Expected behaviour

The toot should be a reasonable height.

Actual behaviour

The toot is very tall.

Steps to reproduce the problem

https://jsfiddle.net/s1on0kdc/1/embedded/html,result/

<p>Normal:</p>

<iframe src="https://mastodon.lubar.me/@ben/101693761835624754/embed" class="mastodon-embed" style="max-width: 100%; border: 0" width="400"></iframe><script src="https://mastodon.lubar.me/embed.js" async="async"></script>

<p>Hidden:</p>

<details>
<iframe src="https://mastodon.lubar.me/@ben/101693761835624754/embed" class="mastodon-embed" style="max-width: 100%; border: 0" width="400"></iframe><script src="https://mastodon.lubar.me/embed.js" async="async"></script>
</details>

Specifications

It appears on every instance I've checked, most using v2.7.3.

I'm using Chrome 72.0.3626.121 on Windows 10