Unicode characters outside the BMP don't display on the webpage

Tweets that include valid utf-8 characters outside the BMP (using surrogate characters) get mauled somewhere along the way to being displayed on the website. Everything after them seems to be not displayed at all. For example, the tweets mentioned in this other issue (they are displayed as funky garbage in search) are displayed as missing in the actual tweet:

http://twitter.com/marnanel/status/10...
http://getsatisfaction.com/twitter/to...

they apparently used to work (the second link says "displays okay" 4 months ago).

here is a newer tweet that has the same problem (everything after the non-BMP character is not displayed on Firefox 3):
http://twitter.com/marnanel/statuses/...