Well there is nothing wrong with the forum software as I've tried it on four different computers and it all works fine, the issue must be at your end but can't think what it is, if everything else is working there is no reason that it shouldn't work.
To see if eveyrthing is working properly you can insert a manual quote, type the below for me in your next post and see what happens, type it exactly as shown but where you see the letters qte please change them for the word quote:
[qte=Joe] Hello [/qte]