(lldb) p _img->GetScalarTypeAsString()
(const char *) $6 = 0x0000000117764473 "float"
(lldb) p padder->GetOutput()->GetScalarTypeAsString()
(const char *) $3 = 0x000000011776446c "float"
(lldb) p voi->GetOutput()->GetScalarTypeAsString()
(const char *) $4 = 0x0000000117764473 "double"
This is unexpected because vtkExtractVOI is supposed to request its output information from the padder.
The only thing i can find is a 12 year old bug (that is still open) in paraview: http://www.paraview.org/Bug/print_bug_page.php?bug_id=380 . One would assume this is something that would pop up more often, not sure if i'm just overlooking something.
The easiest fix would be to just add a cast or work with doubles exclusively. I'll look into it.