Interactive session describing unexpected behavior within pymel

gistfile1.py

    >> import pymel.core as pm
    Warning: file: /Applications/Autodesk/maya2013/Maya.app/Contents/bin/../scripts/startup/initialStartup.mel line 192: Y-axis is already the Up-axis

    ## The matrix initializes as expected.
    >>> spam = pm.datatypes.Matrix(1,2,3)
    >>> print spam.formated()
    [[1.0, 2.0, 3.0, 0.0],
     [1.0, 2.0, 3.0, 0.0],
     [1.0, 2.0, 3.0, 0.0],
     [1.0, 2.0, 3.0, 0.0]]

    ## Now building a transformation matrix.
    >>> eggs = pm.datatypes.TransformationMatrix()
    ## I expect this to take all of the same values from spam's matrix.
    >>> eggs.assign(spam)
    ## Sadly, it doesn't. The middle two rows are missing.
    >>> print eggs.formated()
    [[1.0, 2.0, 3.0, 0.0],
     [0.0, 0.0, 0.0, 0.0],
     [0.0, 0.0, 0.0, 0.0],
     [1.0, 2.0, 3.0, 1.0]]
    ## Trying by another method:
    >>> eggs.data = spam.data
    ## Still nope:
    >>> print eggs.formated()
    [[1.0, 2.0, 3.0, 0.0],
     [0.0, 0.0, 0.0, 0.0],
     [0.0, 0.0, 0.0, 0.0],
     [1.0, 2.0, 3.0, 1.0]]

    ## And here's something that I wouldn't expect to happen at all:
    >>> eggs = pm.datatypes.TransformationMatrix(1,2,3)
    >>> print eggs.formated()
    [[1.0, 2.0, 3.0, 0.0],
     [1.71713525163e-15, -3.53979629992e-15, 1.78748578273e-15, 0.0],
     [-2.94819389609e-15, -6.98692156873e-16, 1.44852606995e-15, 0.0],
     [1.0, 2.0, 3.0, 1.0]]

    ## I would expect the output above to look just like Matrix(1,2,3) considering
    ## that in the source for pymel, TransformationMatrix is a child of Matrix, and
    ## doesn't override the constructor. What's making those middle two rows blow up?