The weld-osgi-core-extension uses direct api calls for checking services and bundles instead of using ServiceTracker and BundleTracker.
The use of this class is not mandatory, but recommanded for such use cases.
The reason is that those classes handle well the dynamism of OSGi, while the existing weld activators may miss events that are sent between the time the list of initial bundles is handled and the time the bundle listener is registered for new events. Simply inverting those calls is not sufficient as you'd have to cope with the possibility to receive events while checking bundles.
I can work on a patch if you want.