Using latest nightly build of SC 9.1 (July 24th) and IE 11, It seems that whenever mouse cursor is moved from a widget on to a piece of svg (contained within a pane following DomIntegration instructions), the event.target is never updated.
In our example, mouse was hovering over button 'Legend', and then it moved down to SVG pane. While the entire cursor was moving around within SVG, its Mouse Event Target still pointed to the button and the button was showing hovered over. I confirmed this by adding a break point inside that button's mouseMove listener.
On Chrome or FF the behavior is correct such that the containing pane of SVG becomes the Mouse Event Target when the cursor moves over.
In our example, mouse was hovering over button 'Legend', and then it moved down to SVG pane. While the entire cursor was moving around within SVG, its Mouse Event Target still pointed to the button and the button was showing hovered over. I confirmed this by adding a break point inside that button's mouseMove listener.
On Chrome or FF the behavior is correct such that the containing pane of SVG becomes the Mouse Event Target when the cursor moves over.