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, Alexandrite, Photon, old-reddit style) are not affected.

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

Example occurrence:

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.

Normal website section.

On sh.itjust.works:
Image On lemmy.world: Image On lemmy.blahaj.zone: Image On lemmy.dbzer0.com: Image

Alternative UI section.

On sh.itjust.works, Tesseract version: Image On lemmy.world, old-reddit style version: Image On lemmy.world, Photon version: Image On lemmy.world, Alexandrite version: Image