To reproduce:
-> Create folder ~/test
-> Start Slicer
-> Download MRHead
-> File -> Save Scene
-> Click "Change directory for selected files" and select "~/test"
-> after selecting the folder and before clicking Save => chmod -w ~/test
-> Click Save
-> When you get the "Cannot write data file" error, click Yes to say you want to continue despite the problem
-> When you get the "Cannot write scene file" error, click Yes to say you ignore these errors and close saving
-> Close Slicer (click Exit and discard modification)

Then, you get the following leaks:

Class "vtkCellData" has 1 instance still around.
Class "vtkInformationIntegerVectorValue" has 3 instances still around.
Class "vtkInformationVector" has 15 instances still around.
Class "vtkPointData" has 1 instance still around.
Class "vtkImageFlip" has 1 instance still around.
Class "vtkTrivialProducer" has 1 instance still around.
Class "vtkMatrix4x4" has 1 instance still around.
Class "vtkPoints" has 1 instance still around.
Class "vtkInformation" has 21 instances still around.
Class "vtkMultiThreader" has 1 instance still around.
Class "vtkInformationIntegerPointerValue" has 2 instances still around.
Class "vtkIdList" has 1 instance still around.
Class "vtkImageExport" has 1 instance still around.
Class "vtkDoubleArray" has 1 instance still around.
Class "vtkAlgorithmOutput" has 1 instance still around.
Class "vtkImageStencilData" has 1 instance still around.
Class "vtkInformationIntegerValue" has 26 instances still around.
Class "vtkExtentTranslator" has 1 instance still around.
Class "vtkImageData" has 1 instance still around.
Class "vtkInformationStringValue" has 1 instance still around.
Class "vtkInformationExecutivePortVectorValue" has 1 instance still around.
Class "vtkShortArray" has 1 instance still around.
Class "vtkVoxel" has 1 instance still around.
Class "vtkFieldData" has 2 instances still around.
Class "vtkInformationDoubleVectorValue" has 2 instances still around.
Class "vtkStreamingDemandDrivenPipeline" has 3 instances still around.
Class "vtkInformationExecutivePortValue" has 4 instances still around.