This seems to be related to DataFrames, (or rather DataArrays). Often such issues will arrive at an update, and be fixed when you update again. If you make sure you are on the last version and the problem persists, you should report it in the DataFrames.jl issue tracker.
- [julia-users] bizarre warning messages Tony Fong
- Re: [julia-users] bizarre warning messages Mauro
- Re: [julia-users] bizarre warning messages Ivar Nesje
