Assigning with .loc throws SettingWithCopyWarning despite following instructions in warning
Happens with some data frames only. I cannot produce a minimal reproducible example, but can pickle the data frame in question if it helps.
![warning_with_loc](https://user-images.githubusercontent.com/11860098/61002969-6dc58480-a36b-11e9-8655-607d20f664a9.png)
