1) JavaDoc AjaxBehavior.isImmediateSet():
Tests whether the immediate attribute is specified. Returns true if the immediate attribute is specified, either as a locally set property or as a value expression. This information allows an associated client behavior renderer to fall back on the parent component's immediate status when immediate is not explicitly specified on the AjaxBehavior.
myfaces don't implement this feature in HtmlAjaxBehaviorRenderer
2) isComponentImmediate use introspection for evaluation of isImmediate - that is unefficient (Contains code comment: Currently implemented by ActionSource and EditableValueHolder but we cannot be sure about both interfaces so lets make introspection calls here - but what means "we cannot be sure about both interfaces" ?)