AudioServerPlugIn: HALC_ProxyObject::GetPropertyDataSize ('stm#', 'inpt', 0, AI32) error ('who?')

As soon as my AudioServerPlugIn (as well as all samples from Apple, e.g. NullAudio or SimpleAudio) is installed, I see the following errors in Console.app: default 19:43:34.953638+0200 systemsoundserverd HALC_ProxyObject::GetPropertyDataSize ('stm#', 'inpt', 0, AI32): got an error from the server, 0x77686F3F error 19:43:34.953574+0200 coreaudiod HALS_Object_GetPropertyData_DAI32: the object does not implement the property default 19:43:34.953814+0200 systemsoundserverd HALC_ProxyObject::GetPropertyData ('stm#', 'inpt', 0, DAI32): got an error from the server, 0x77686F3F (Those 4CCs are kAudioDevicePropertyStreams and kAudioObjectPropertyScopeInput) But looking at the code, HasProperty / GetPropertyDataSize / GetPropertyData all seem to be implemented correctly (same as they are for NullAudio) for those, but this error still seems to get thrown. The same is true for the NullAudio sample. (I'm not even sure they're from the AudioServerPlugIn, but if I remove any HAL drivers and relaunch coreaudiod, then the messages disappear. Does anyone know what the actual requests might be? Debugging (or even just logging) from an AudioServerPlugIn seems impossible, so I cannot really debug or log to see which queries arrive at my plugin to see what I might be missing. Does anyone have any ideas?