Having this e.g this class:

public class BeanDefault<T extends AbstractClass> {
}

and its specialization like this:

@Specializes
public class BeanCustom<T extends AbstractClass> extends BeanDefault<T> {
}

will result in:

Caused by: org.jboss.weld.exceptions.DefinitionException: WELD-001511: Specializing bean Managed Bean [class mypackage.BeanCustom] with qualifiers [@Any @Default] does not have bean type class mypackage.BeanDefault<T> of specialized bean Managed Bean [class mypackage.BeanDefault] with qualifiers [@Any @Default]

This is IMHO inappropriate since the type BeanDefault<T> is present. CDI spec says just:

Formally, a bean X is said to specialize another bean Y if either:
...
Furthermore, X must have all the bean types of Y. If X does not have some bean type of Y, the container automatically de-
tects the problem and treats it as a definition error.