Appearently so. Haven’t done much testing but it’s a b*tch when half of your post is stripped with no warning and notification because you added an emoticon like a : ) or a : o (without the space). Sometimes the emoticons are simply stripped from the post and sometimes all the content succeding the emoticon is also stripped with it. Weird one.
Note that these incidents occoured on their mobile optimized website; not sure if it’s the same for the native iPhone app..