Cannot adjust data hierarchy in DataModule

I want to try image-guided surgery using slicer developed module.

The main Notes (displayed in data module) include :

  1. Ultrasound ( vtkMRMLVolumeNode , real time transmission by openigtlink module through a image grabber connected with ultrasound machine)

  2. ImageToProbe (constant linear transform), ProbeToTracker (real time linear transform acquired by NDI and transmitted by openigt module ) Their data type are both vtkMRMLLinearTransformNode.
    And with the help of openigtlink module, the hierarchy in Data module likes:


In oder to  realize the function of image-guieded surgery, I need to transform Images (Ultrasound) from image coordinate system to tracker coordinate system. so I choose to adjust  hierarchy ( draging nodes):
|------ImageToProbe (success)
|----------Ultrasound (fail)

I have tried many times, but failed to drag "ultrasound "node to the lower level of ImageToProbe node.

More details about my system configuration are:
Windows7 Slicer 4.5 Visual Studio2013


Hi! This was a known issue but it has been fixed since the release of 4.5 that was two years ago. 4.8 was released yesterday, please try with that. Thanks!