Adding a Legend Field Disables Tooltips for Area Charts

Hello,

I have a pretty standard dataset with three fields: a time field, a quantity field, and a categorical field. When use an Area Chart and put the time field on the x-axis and quantity on the y-axis the default tooltip shows up fine when I hover over the visualization. However, when I add the categorical field to the legend the tooltip disappears. When I change the visualization type to a Stacked Area Chart though the tooltip comes back and functions fine. 

Is this the correct behavior? I assume not since I've seen tooltips work before with Area Charts with a legend. Maybe it's a bug? If so are there any known workarounds?

Thanks!