one can see posts with proper quoting format as well as posts that, for one reason or another,
I've had similar problems, not only with quotes, but links, italics, etc., in posts I'm making. They appear correctly when previewed, but when posted the text appears between the bracketed code, but it's still just text.
As an experiment, I'm posting this from my wife's laptop, instead of the desktop. That might demonstrate that it's something within the particular computer that's responsible, or not.
On edit: Nope. Still the same problem...