Hi Tstief,
The issue you posted is related to modifying tags using third party application written in .Net and would be better suited in the MSDN community. Please visit the link below to find a community that will offer the support you request and post your issue.
http://social.msdn.microsoft.com/Forums/en/windowsgeneraldevelopmentissues/threads
Thanks and Regards,
Srinivas R
Microsoft Support.
Visit ourMicrosoft Answers Feedback Forum and let us know what you think.