StackedBar tooltip title shown as literal text "tooltip" instead of actual label until hovering over second stack

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Describe the bug
The tooltip title is shown as the literal text "tooltip" instead of the actual label until you hover the mouse over the second stack of stacked bar.

After moving the mouse out and back again, it does the right thing the second time (see animation below).

Screenshot

first time down after loading the page, it shows "tooltip" over the blue part, then switches to "normal" when hovering over the red, then I move the mouse away and back again and it still shows "normal".

How to reproduce
Works with the same one from my other issue :) https://jsfiddle.net/3dpbg241/