REGR: if someone wants to find where this was fixed would be gr8
Regression from 0.16.2 to 0.16.1, but fixed in master, doced here: https://github.com/pydata/pandas/commit/2748e82ae99511f23f0f5134332706bde0798ef5

xref #10979 #9345 

Ideally want identify where this happened, and if we have enough test coverage.
