I've tried to get the Twitter Tools tweet prefix to function, but it not seem to work.

I have set the prefix to "post", but what I now get is that all my tweets starting with "post:" won't convert into posts, but all the other tweets do.

I'm in understanding that it should post ONLY those tweets starting with the given prefix, but seems now to do the quite opposite. Have I understood something wrongly or does my configuration have something wrong?

In my configuration I have:

Enable option to create a tweet when you post in your blog? Yes
Tweet prefix for new blog posts: post
Set this on by default? Yes
Create a blog post from each of your tweets? Yes

Is this how it should be?