Integrating with Twitter Service - NOT tweeting every blip?

According to the services page - You can prevent updates from being sent on a blip-by-blip basis by starting your message with "!". However, when I tried doing a blip and putting ! before my message to avoid tweeting it, it still showed up as a tweet in my twitter stream. Am I doing something wrong?

Here's the link to my blip, if you want to check how I added the !.
http://blip.fm/profile/rossruns/blip/...

In the meantime, i'm just disabling the twitter service, and only re-enabling for blips that I want to post to my twitter stream.