New Post: Problem when logging in again

It seems like I found the problem..
If I debug the Application the Tweetinvi.TwitterCredentials Object contains "ApplicationCredentials" "Credentials" and "CredentialsAccessor" directly after the re-login.
After some time in another thread the "Credentials" value is NULL. If I do something like this (in the current Thread):

TwitterCredentials.SetCredentials(TwitterCredentials.ApplicationCredentials);

The Application works fine again.

Is there something I did wrong in the re-login procedure so that the data is not available to all threads?