incorrect behavior of string-indexed Series
The following code gives "IndexError: Out of bounds on buffer access (axis 0)"
(pandas version: 0.12.0, Python version: 3.3.2, OS: Linux):

pandas.Series([0], ["y"])[["x", "x", "y"]]

If "x" is replaced to 1 and "y" to 2, then the error disappears.
