When the data of a VALUETYPE_MULTIPLE control is saved, the data is handled by the processMultiple() method in the SaveHandlerImpl class. This class first deletes the contentNode with the name of the control, then creates a new one and fills in the node data from the submitted dialog form.

The problem here is that by creating a new contentNode we also get a new UUID... and when activating the modified node containing this contentNode you will end up with a node containing multiple contentNodes with the name of the control.

The correct way of handling this would be (if I'm not totally mistaken):

1. leave the contentNode as it is
2. remove all its nodeDatas
3. add the new nodeDatas from the submitted dialog form