Post formatting is often screwed up for me. Spacing between paragraphs gets doubled. If I delete a full line, the text below it changes size and/or font. It's not uncommon to see tags that I didn't intend to add in the first place show up without getting closed properly, leaving ugly </whatever> tags in the resulting post...
I'm using Chrome on a Ubuntu OS, and it doesn't seem to matter if I use Quick Reply or the full option.
Sometimes I edit posts to remove the excess junk, and that seems to work fine. Sometimes I just don't worry about it. Not really a big deal.