I would recommend you to read our help article
that gives some additional information about expanding nodes and why programmatic expanding does not fire both client-side and server-side expand events. Please try to use both client-side and server-side approaches for explicitly expanding nodes and right after that place the code that is to be executed in that event.
the Telerik team
If you want to get updates on new releases, tips and tricks and sneak peeks at our product labs directly from the developers working on the RadControls for ASP.NET AJAX, subscribe to their blog feed