This behavior occurs in a very specific setup and it cannot be isolated easily. Currently, it is reproducible in RadMap when you use RadToolTipService to set a tooltip to an item in the VisualizationLayer. If you hover the item and zoom in or out without moving the mouse (without hiding the tooltip), the tooltip popup is still displayed, but its content is empty.
To work this around, use the WPF's native ToolTipService. If you want to be consistent with Telerik's theming, you can use the RadToolTipContentView as the ToolTipService.ToolTip value.
Several WPF windows are created - each on different UI thread.
RadToolTipService is used in each window to show tooltips.
When user moves the mouse over all windows - an exceptions occur
The root cause of the issue are static members in the RadToolService class.
InvalidOperationException ("The calling thread cannot access this object because a different thread owns it") is thrown when a tooltip is opened an a UI thread different than the original UI thread. Available in LIB version: 2016.2.620
Available in Q2 2015 Official Release.
RadToolTipService generates System.ArgumentNullException when it is used in Adorner (e.g. RadRibbonView.Backstage). Attached is a xaml example demonstrating the exception. Available in LIB version: 2014.3.1402
The ToolTipContent is not displayed when it is bound to a UI element's property with ElementName. The fix is available in LIB Version 2014.3.1319.