I do believe this is a bug, but I might be missing something.

For a deployment with beans A and B where B @Specializes A, if you veto() PBA<B>, you can now observe dual notification for PIT<A>.

Here is the relevant code - link.
We should IMO extract PIT invocation outside of this method which is re-invoked if you veto specialized bean (link).

There is a TCK test where this behavior can be spotted if you add an observer for PIT<Bravo>>, see org.jboss.cdi.tck.tests.full.extensions.lifecycle.processBeanAttributes.specialization.VetoTest.