From the change in https://github.com/JuliaData/Tables.jl/pull/255, we're considering the fact that Tables.Columns didn't call Tables.columns a bug, so it's being changed and you don't need to call Tables.columns yourself anymore when using Tables.Columns. Luckily, I'm not aware of any table inputs where this actually makes a difference (i.e. a table where Tables.columns(x) !== x), so this shouldn't be very disruptive.
From the change in https://github.com/JuliaData/Tables.jl/pull/255, we're considering the fact that Tables.Columns didn't call Tables.columns a bug, so it's being changed and you don't need to call Tables.columns yourself anymore when using Tables.Columns. Luckily, I'm not aware of any table inputs where this actually makes a difference (i.e. a table where Tables.columns(x) !== x), so this shouldn't be very disruptive.