Problems with publishing using multiple WordPress accounts

I have setup Microblog Poster to publish posts to one Facebook page.
After setting up the Facebook app and authorize the account I published a test post and everything is fine.

But when my partner logs in with his WordPress account (same user level, we both have administrator privileges) and publishes a new post nothing arrives on Facebook.
There is no error message, no error in the server logs and even the Log/History of Microblog Poster doesn′t show up any information.

Just to clarify:
Is Microblog Poster able to run in a multiple user enviroment?

Is there something I missed in the setup?