Facecount in MeshBuilder.addIndices vs MeshBuilder.setIndices

[fieldOfView]

MeshBuilder.addIndices vs MeshBuilder.setIndices both set the self._indices to the input indices argument (so I am guessing they expect the same input), but they calculate the new self._face_count differently:
https://github.com/Ultimaker/Uranium/blob/master/UM/Mesh/MeshBuilder.py#L124
https://github.com/Ultimaker/Uranium/blob/master/UM/Mesh/MeshBuilder.py#L352

When using addIndices the resulting facecount seems to be 3 times that of when using setIndices. Either one of them is doing it wrong, or some documentation is needed to explain why there is a difference.