I have created a Vaadin application with Vaadin-CDI and observer method in a @ViewScoped bean not executed when an event fired when this observer declared as @Observes(notifyObserver=Reception.IF_EXISTS) and the bean exists in that scope.
@ViewScoped is a Vaadin specific pseudo-scope created with DeltaSpike.
I have created a Vaadin ticket, but that resolved to DeltaSpike issue and that resolved to WELD issue.

I have tried to upgrade weld-core in JBoss to 1.1.28.Final but observer still not executed.

I have tested it with WELD 2.1.2 on WildFly and there the observer is executed as excepted.