Exception Days in the Workload Planner do not work properly


I have just tried to set an exception day for the Workload Planner. But it had no effect. I set the volume for this date to zero, but the jobs allocated to this date were not moved, even though the schedule is free enough around this date. 

Later I tried to change manually the allocation from the Workload Planner tab in the Job Details, but it changed nothing as well.

Am I doing something wrong?