This is reproducible only when the chart's automation peers are used. For example, they are used by default when you use the chart on a touch screen. Or when an accessibility tool is used on the application with the chart.

You can work it around by disabling the auto peers (http://docs.telerik.com/devtools/wpf/common-ui-automation).

AutomationManager.AutomationMode = AutomationMode.Disabled;