I am having the same issue right now and was wondering if a solution was ever found? I tried the bbpress-do-short-codes plugin and it seems to work for google chrome, but not firefox. I would ok to just disable image captions from the tinymce editor too. I’ve been trying to figure out the css code so I could just slap it with a display:none, but haven’t had any luck.
I guess I jumped the gun on asking for help on this. A little more digging and I found my answer. I found a way to automatically load my default style sheet in place of the tiny mce style sheet and this basically automatically styled the editor to look like everything else.
Just had to add this to my functions.php:
if ( ! function_exists('tdav_css') )
$wp .= ',' . get_bloginfo('stylesheet_url');