Dragging does not work in Layer Manager

When dragging a layer within the Layer Manager an exceptions occurs:
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at org.esa.beam.visat.toolviews.layermanager.MoveLayerDownAction.canMove(MoveLayerDownAction.java:47)
at org.esa.beam.visat.toolviews.layermanager.LayerManagerForm.updateFormControl(LayerManagerForm.java:203)
at org.esa.beam.visat.toolviews.layermanager.LayerManagerToolView.layerSelectionChanged(LayerManagerToolView.java:62)
at org.esa.beam.visat.toolviews.layermanager.AbstractLayerToolView.setSelectedLayer(AbstractLayerToolView.java:134)

The tree ui stays unchanged.
The exception is thrown when the layer is selected after dragging.
The Layer Manger is not usable at all after this exception.