In IE11 the anchor of a Tooltip rendered in a container that has any parent that is positioned by CSS transform is wrong. It acts as if the parent was not moved.
The problem appears to resolve if the position: fixed style is changed to position:absolute. This style is contained in the .__react_component_tooltip class.
I can confirm that in IE11 some of the examples on the react tooltip example site do not work. In particular those who have a parent with a css transform.
FYI - it appears one solution for this is creating the tooltips outside of the modal, and then in the modal's componentDidMount() method, you call tooltip.rebuild()
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The problem appears to resolve if the
position: fixedstyle is changed toposition:absolute. This style is contained in the.__react_component_tooltipclass.