Angular-ui's tooltip does not display correctly in ng-grid

Angular-ui's tooltip does not display correctly in ng-grid

I've been searching for some time for a solution for displaying a tooltip
on ng-grid but with no luck. When I use the cellTemplate on ng-grid for
customizing the cell to include a tooltip I have experienced various
problems - the tooltip is either not showing up or behaving strangely as
shown in a plunker: http://plnkr.co/edit/MFhwgOvSUFKcyJPse5wf.
Have I missed something? Does anyone have a solution for displaying
tooltips nicely in ng-grid?
Best regards.