These seem to be the leading cause of edit corruption right now.
<embed> tags: https://pt.wikipedia.org/?diff=39696565
I'm thinking we should put in hacks to remove these kinds of tags. Maybe at the point where we serialize the HTML and send it to Parsoid (ve.init.mw.Target#getHTML). If these tags are added immediately upon document creation (we'd need to get our hands on one of these bad plugins to test that) we could also consider trying to work around this in ve.createDocumentFromHtml instead. I suspect, though, that these tags are probably added asynchronously, and probably only in cases where we fall back to the iframe trick because DOMParser HTML support is not available.