hm i fear this is by design and to get the old behaviour back it’d require a hack. the whole input device system was redesigned in beta32 and is now event based, which means that input device sink nodes like the split node subscribe to an input device and start to listen to its device messages. what we see in your patch is that whenever the input of the join node goes from nil to some value a new mouse including its event stream gets created, but as no one listens to its messages yet the mouse button/move message simply arrives nowhere.
can you describe the problem you’re trying to solve a little more? maybe there’s a different solution available.
I’ve changed the way the MouseStates (Mouse Join) node works so new subscribers downstream will also get notified about the state change observed in the current frame. Your test patch works just fine now. Check latest alpha build.