Serious Floating point error v 0.16.2 and v0.17
Python 3.4.3/64bit, Pandas 0.16.2 or 0.17

The operation is a addition. The results of the first two rows are correct most of the time, on occasion a value 1.5-315 appears. Every test performed with same input. Fail rate is about 3-5% of the time.

df['v1']+=10.0

I copied the dataframe results to numpy and perform the same addition with same values and it works correctly every time.

npyarr=df.reset_index().values
npyarr[:,1]+=10.0

After a few weeks of noticing these symptoms it appears to only affect the first two rows every time, the data frame has thousands of rows.
