By default Discourse displays part of a page that is linked, via a URL on a single line, and the developers appear to think they have solve the mixed content issue this can cause, however the Quoting for PLANET topic generates mixed content warnings so it clearly isn’t solved.
There are some work arounds for this:
- Don’t post non-HTTPS URLs on single lines
- Have an admin add a space to the start of any HTTP URL on a single line
Neither of these are ideal, I have posted to the Discourse site about this but since most other threads on this issue are locked I’m not very optimistic there are are answers other than 1. and 2. above…