.ix strange bug for float index
In [1]: import pandas

In [2]: index = [52195.504153, 52196.303147, 52198.369883]

In [3]: a = pandas.DataFrame(randn(3, 2), index)

In [4]: a
Out[4]: 
                     0         1
52195.504153  1.367681  0.243237
52196.303147 -0.745796 -1.054106
52198.369883 -1.462461 -0.683286

In [5]: a.ix[52195.:52196.]
Out[5]: 
Empty DataFrame
Columns: array([0, 1])
Index: array([], dtype=object)

In [6]: a.ix[52195.1:52196.5]
Out[6]: 
Empty DataFrame
Columns: array([0, 1])
Index: array([], dtype=object)

In [7]: a.ix[52195.1:52196.6]
Out[7]: 
                     0         1
52195.504153  1.367681  0.243237
52196.303147 -0.745796 -1.054106
