live.observer 'property cannot be listened to' error

I'm getting this message in the Max window for most of the paths I send to live.observer.

My path is: live_set tracks 0 clip_slots 2 clip, so it seems like it should be pretty simple but I'm getting this message for the property "is_playing" and pretty much any boolean property. The only ones that provide any info are the function properties. However, the general "is_playing" property (as it applies to Live's master transport) does give the correct result.

With the same path / id, live.object also provides the correct status, but I need the updates to be continuous without having to ask it for info all the time.

Any ideas? I feel like I must be missing something here - totally stumped!