The crosshairs in line charts and sparklines do not disappear reliably. This behavior is apparent even on the demo page for sparklines. The result is that there is an extra vertical bar that is stuck on the chart. Hovering over the chart again sometimes fixes the issue.
This behavior can be confusing to a user if the crosshair remains stuck at the end of the chart and the color of the lines look similar, it may look like the data drops off at the end.