The mechanism that defines a node order in tree branches is now broken and needed to be fixed. It is the SortingValue member of vtkMRMLHierarchyNode.

There are two issues

• SortingValue is not changed on drag&drop any more (SetIndexInParent should be called but it's not). It should either be handled at the lower level functions like dropMimeData where we have the row number, or in reparent, but then we need to pass the row number so that it can be used for setting the SortingValue (see desiredNodeIndex in qMRMLSceneModel.cxx, which does not work any more)
• In parenting the sorting values are handled as integers that can be increased freely (see MaximumSortingValue), and in SetIndexInParent it is handled as a floating point value ranging from 0 to 1. This seems to be a problem (see SetIndexInParent where in case of 0 new index, sorting value is just decreased by one, although it could have a wide range of integers)