Before I explain, I want to say that the undo/redo will be very appreciated. There is a minor bug that probably should be fixed. Please excuse me if I don't use the correct terminology.
I noticed that the undo buffer is not cleared when I cancel a message. It might not be cleared when a message is posted, but I encountered the problem when I began creating a reply then I cancled the reply. When I did multiple undos, I got content successive to the beginning of when I began using the forum, not from the beginning of when I began a specific message. In other words, the undo buffer included content from messages I had been editing prior to the message I was currently editing.
I hope you understand. I assume it will be easy enough to re-create.
I am sorry, perhaps I need to explain that I encountered the problem when I was using the sandbox forum for the new forum software. Note that I got to this forum from the message about the new forum software; it did not say anything about the forum for reporting bugs.