According to normal behavior of WPF window, Loaded event occurs when the element is laid out, rendered, and ready for interaction.It is the last event raised in an element initialization sequence. Where as in RadRibbonWindow I have observed that the Loaded event is the first one to be called, even before the Window is shown at all. And when loaded event finished its work then Window appears on screen with all its content loaded. This behavior confuses with the description of Loaded event here https://docs.microsoft.com/en-us/dotnet/api/system.windows.frameworkelement.loaded?redirectedfrom=MSDN&view=netframework-4.7.2 ?