Another example of problems…
I was editing a page last night and specifically wanted two ‘definition’ lists – not the more common ordered/unordered lists provided by the visual editor. No problem – I produced what I wanted in the HTML editor. Everything rendered fine when previewed. The list was tweaked and reviewed several times more and everything remained laid out as I originally typed it, making the ongoing editing process easy.
Then, a little later on, I swapped into the visual editor and then back to the html editor. Now, everything in my lists had been collapsed into single paragraphs/blocks of text. They still functioned when previewed, but the page will be a bitch to edit if/when I return to extend them in the future.