I've ran into a couple of BBCode saving issues, specifically when I was writing this post here (https://forums.computercraft.cc/index.php?topic=616.0). Upon clicking "Save Draft", it seems to insert an absolute *ton* of spoiler tags, and completely ruins the formatting.
It also changes
[spoiler=Command Line Arguments] into
[spoiler="Command Line Arguments"] which then puts those quotes into the spoiler title:
I expected "Save Draft" to keep my topic as-is, rather than changing it so drastically. If you want to test this, just copy the raw text from the above-linked post (if you have access to that data, otherwise DM me and I can send it), then put it into a new post and click "Save Draft" then "Preview" -- you'll see how insanely it screwed up the post.