@elcollie,
In case of column chart, toolTip is shown only when you mouse-hover on specific dataPoint, which is difficult in case of line-chart, so the behavior is designed to retain the toolTip even when you are away from the dataPoint but within the plot-area. However if you like to hide toolTip on moving out of dataPoint and show when you hover on dataPoint, please take a look at this JSFiddle.
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Priyanka M S
Team CanvasJS