Reply previews mix up bi-directional (rtl-ltr mixed) text

[ghost]

Fairly simple in demonstration: I typed out:

كيف نقول 'jorts' في العرابية؟

(Github itself appears to mix this up, my apologies.)
In posts and the text entry box, it shows as intended:

In the reply preview box, it shows as this instead:

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• I searched or browsed the repo’s other issues to ensure this is not a duplicate.
• This bug happens on a tagged release and not on master (If you're a user, don't worry about this).