I just quoted the first part of "Updating static files with legacy bundle in Plone 5" (marking the portion with the mouse and clicking into the shown "quote" action). The quoted portion contained a bulleted list. However, the corresponding markup in the quote is missing (given a quite unreadable presentation).
Thanks for reporting!
We have no special plugins installed which might introduce such a problem. We are running a recent version 1.8.0.beta7, but still beta, so this may happen.
So I would say this is an upstream problem in Discourse. You may want to check if it is already reported at https://meta.discourse.org/c/bug
There are about 50 quoting related bugs known -- among others: wrong quoting for quotes, hyperlinks and lists.
The list related quoting bug is very similar to what I report in this topic (even though the wrong layout is a bit different). It was reported about 1 year ago.
Seeing this huge number of quoting related bugs gives me the feeling that something is fundamentally wrong (i.e. on the conceptual level): it looks as if "partial quoting" (in contrast to the quoting of a complete post) were using the same approach as that used for moving information from the browser into a different application: tell the browser to put the text (without layout) into the clipboard and take this text out of the clipboard at the target location -- as the target application cannot be assumed to understand html markup, the browser will place markup-less text into the clipboard -- and consequently, large markup parts are lost. Looks as if something like this happens at least for "partial quote"s.