Hello. I noticed that copying text around doesn't really work anymore in the new wikitext editor.

List of steps to reproduce (step by step, including full links if applicable):

• Enable beta-feature "2017 wikitext editor" [https://de.wikipedia.org/wiki/Spezial:Einstellungen#mw-prefsection-betafeatures]
• Use skin "timeless" [https://de.wikipedia.org/wiki/Spezial:Einstellungen#mw-prefsection-rendering]
• Edit source of an article
• copy text into the article

What happens?:
The copied text appears in the textbox, but not in the preview
Here is a video of what it looks like: https://cdn.discordapp.com/attachments/653246272266043404/856858659316039710/2021-06-22_13-26-23.mkv

What should have happened instead?:
The copied text should also appear in the preview

Software version (if not a Wikimedia wiki), browser information, screenshots, other information, etc:

• Firefox 89.0.1 with disabled uBlock origin