I've enabled tables in the purifyer for now, that should take care of it.
Well, it kinda-sorta helps. The problem now is that the table structure is so character-intensive that it's blowing through the 5k character limit after just 4 or 5 notes. I copied 13 scribe notes to the clipboard and pasted them into the editor. when previewing it, it cuts the message halfway through the 5th scribe note. If you paste the 13 scribe notes, view the source, then copy the source into another editor to view the character count, you see that it's almost 14k characters. Due to the formatting.
It looks like the message system is taking the first 5k raw characters, truncating the rest, then sanitizing it. It should do it the other way: Sanitize to get rid of the cruft, then truncate what's left over. After previewing the scribe notes message, a source code view of the 4.5 scribe notes that didn't get truncated showed that it was only only about 800 characters. There's no reason it should have been cut there.
This is also causing problems with copy/pasting messages, too, since those are encapsulated into table cells. I copy/pasted four messages and previewed them. They were truncated after only ~2,400 visible characters. The rest of what was filling out the 5k limit was all invisible table markup and formatting.
If we're planning on keeping this style of rich text in the messaging system, then I think we really need to look at significantly increasing the message size limit to compensate for the overhead of the HTML markup in the messages.