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.