Thanks for your comments Adai. The re-created relationship (done using the snapvault start command) isn't showing up in the external relationship tab. I removed the relationship using PM GUI and nothing else. Currently the QTree I want to add to the dataset ins't part of it but it was previously.
Can you tell me in more details how I have to deal with the dfpm dataset relinquish command?
Entered dfpm.exe dataset relinquish %qtreename%
and got following Error: Could not find volume or qtree '%qtreename%'. Reason: There is no host, aggregate, volume, qtree, resource group, or dataset named %qtreename%.
Question for me is why does PM find a relationship which got deleted?