Quotation marks and other symbols are incorrectly rendered

Quotation marks and other symbols, when typed in the title of a spoiler tag, show up as broken HTML entities.
This only happens on the normal website. Other Lemmy UIs (Tesseract, old-reddit style, Photon, Alexandrite) are not affected.

Examples of characters:
" becomes "
& becomes &
< becomes <
> becomes >

Example occurrence:
::: spoiler quote, ampersand, less than, greater than " & < > Expected correct result: " & < >
Expected erroneous result: " & < >
:::

Warning: The following spoilers contain full-page screenshots of the phenomenon in question. Do not open on a slow or metered connection.