Rather than start a new topic, I'll just use some thread necromancy here...
I've had on several instances when attempting to quote a user via quick reply go a bit haywire. What would happen is I quote say... Nattey Poot Poo and then use preview because I wanted to bold something or whatever. When I then clicked on Post, the message I typed would essentially disappear and I would be looking at a "post new topic" screen. It's not a constant thing, but does happen from time to time. Just an FYI I guess, maybe it's user error