No markdown inside spoiler tags will be likely be an issue for other posts too. (EDIT: found one)

As for Trending Communities I was mainly trying to use the tags to create an expandable section, like this:

But what Connect does (blocking all the text) isn't technically wrong, so it's understandable if you don't want to change it. Auto-TLDR bot often uses the tag for the same effect, but maybe we should both wait for a new, more appropriate Markdown feature, rather than (ab)using the one for spoilers.