If one of the axes in a 3D plot is a date axis and the data for this axis consists of Date objects, the hoverinfo is displayed as `NaN, 0NaN, aNaN:aN`.  [Codepen](http://codepen.io/anon/pen/RpbQWQ) When the date data is provided as date strings, these strings are displayed in the hoverinfo instead, instead of being parsed and formatted as dates.