This may be stupid but, when I select an element in Chrome/Chromium, and enter "Edit As HTML", the secondary click menu gives no option to paste anything as plain text. If I click Ctrl+V, as long as Ctrl is down the editor is deactivated, so I still can't paste anything.
I can only have "paste" and "paste as plain text" options when I edit a attribute, which isn't very helpful when I need to paste multiple lines of code.
The same problem is experienced under Linux and Windows. Not sure about Mac.