The drop from ModelExplorer to an ActivityPartition in the diagram is allowed but the inPartition field is not set

Step to reproduce :

1. create an Activity diagram
2. create an ActivityPartition in the diagram
3. create an ActivityNode (eg. CallOperationAction) in the ModelExplorer
4. drop the ActivityNode inside the ActivityPartition

-> this is allowed but neither the inPartition field of the ActivityNode neither the nodes feild of the ActivityPartition are set May be this action should not be possible at all