Hi, Ulrich. It works without problem after restarting my Notes client.
Did you get any error message after saving your configurations in preference page?
Usually, the configuaration of a custom plugin will be saved under "X:...\Data\workspace.metadata.plugins\org.eclipse.core.runtime.settings". The file(de.pavone.taskmanagement.prefs) under this folder contains your configurations, such as username and so on.
Under "X:...\Data\workspace.metadata.plugins\de.pavone.taskmanagement\your name" you can find the file contains services you added and other necessary files at runtime.
Please have a look, whether all of the setting files will be generated after closing your Notes client.
Looking forward to your more details about this problem. Thank you.