Group By Apply Occurring Twice On First Item - Pandas

02 Oct 2014 https://github.com/pydata/pandas/issues/7739#issuecomment-48823964

If Pandas's Group By is applying the function in Apply twice to the first item, it's actually expected behavior according to the warning in the documentation: http://pandas.pydata.org/pandas-docs/stable/groupby.html#flexible-apply