JP, I tried to reproduce this in the test forum, but without success. Tried FF10, IE9, and Chrome and every single time using preview and edit several times, and it displays the confirmation every single time.
How often does this happen to you?
You've been actively posting in the forums for years and I doubt if this is what you are seeing... but I figured I'd mention it --sometimes when the reply form sits up high in your browser window and you submit your post-- the submission form will close and display the confirmation message up top and outside of the viewable browser window, so you may miss it. Do you think that is the case here?
when responding to a post, I preview my post and click the submit button, it is not acknowledged....however if I reload the page, the post I made is displayed.