Test cases shouldn't be added to a complete test suite and when a Query Based Suite is marked as complete the query continues to run and more test cases are being added to the suite. TFS needs to stop running the query for query based suites when they are marked as complete, or prevent test cases from adding to a completed test suite (Query or Static).
Team Explorer VS2013 TFS 2010 - TF30063
TF30063 when changing Notification URL
Useful to allow tasks to be 'unassigned'
Cannot add TFS server group to Access Level
unable to see build step logs, tfs 2017