Earlier quoted context omitted.
Microsoft has been doing this for decades. Ever try to collaborate on a web project using MSN Messenger? Every message you sent that contained 'index.php' was mysteriously dropped. It IS Orwellian, but you should not be surprised. The big communication services all seem to have their own little moral or technical hacks they use to keep your discussion limited and away from certain topics / words.
It is even worse than that -- it also seems to automatically insert graphical smilies whenever it sees what it thinks is a text smiley. Makes it very hard to cut-n-paste a code fragment. Of course you can turn this off, but only on the receiving side -- if you are sending someone a command or piece of code (that contains parentheses and colons), you have know idea if their end will convert to the graphic smilies, and…
On the other hand, the issue above represents a horrible failing on the part of MSN as a network/protocol. Silently dropping messages without giving error to either party is insanely stupid behaviour, and MSN's done it frequently for as long as I can remember.