You can edit two posts in the same Q&A thread at the same time without submitting.
If you start editing the first post with big changes, then notice a quick fix for another post with small changes and start editing that as well, you will be fooled into thinking that clicking "Save Edits" below the second post you just edited will indeed save the second post. Instead the post being edited first will be the one submitted.
That is probably not a very common scenario but clearly a bug.
(Using the built-in browser editor on Safari 11.1.2)
"Save Edits" below a post should always save the edits that are in that post that this button is below of.