After analysis, I've found out that NPEs were caused by NULL values being cached and nodes from MIX were loaded due to the fact that PubSub event (also fired in MIX) were propagated also to PubSub component. I've modified source code, to add filtering of PubSub events based on componentName, so that if PubSub component named pubsub fires an event it will be processed by all handlers but it is possible to filter out events coming from the component with a different name.