AudioUnit: Error reported by mediaserverd - "Error 'what' getting client format for physical format"

Question

I have a VOIP application that uses AudioUnit. On iOS 9, I see an error message that says the following. I do not see this in iOS 8:

mediaserverd[43] : 13:16:38.880 ERROR: [0x1f72d000] >va> 500: Error 'what' getting client format for physical format [ 16/44100/2; flags: 0xc; bytes/packet: 4; frames/packet: 1; bytes/frame: 4; ]

Does anyone know what this means? The audio seems to work fine, but I'm still a bit irked by it and would like to address it if I can. My AudioUnit setup code is below. Help appreciated. Thanks.

CheckError(NewAUGraph(&audioState.graph), "NewAUGraph failed");

AUNode rioNode;    
AudioComponentDescription desc;

desc.componentType = kAudioUnitType_Output;
desc.componentSubType = kAudioUnitSubType_VoiceProcessingIO;
desc.componentFlags = 0;        // Documentation states "Set this value to zero"
desc.componentFlagsMask = 0;    // Documentation states "Set this value to zero"
desc.componentManufacturer = kAudioUnitManufacturer_Apple;

CheckError(AUGraphAddNode(audioState.graph, &desc, &rioNode), "AUGraphAddNode failed for RIO");
CheckError(AUGraphOpen(audioState.graph),"Failed to open graph");
CheckError(AUGraphNodeInfo(audioState.graph, rioNode, NULL, &audioState.rio),"Failed to get rio node info");

UInt32 flag = 1;
CheckError(AudioUnitSetProperty(audioState.rio,
                                kAudioOutputUnitProperty_EnableIO,
                                kAudioUnitScope_Input,
                                1,
                                &flag,
                                sizeof(flag)), "Enable IO Failed");

AudioStreamBasicDescription audioFormat;
size_t bytesPerSample = sizeof(SInt16);
audioFormat.mSampleRate         = 8000;
audioFormat.mFormatID           = kAudioFormatLinearPCM;
audioFormat.mFormatFlags        = kAudioFormatFlagIsSignedInteger | kAudioFormatFlagIsPacked;
audioFormat.mFramesPerPacket    = 1;
audioFormat.mChannelsPerFrame   = 1;
audioFormat.mBitsPerChannel     = 8 * (UInt32)bytesPerSample;
audioFormat.mBytesPerPacket     = (UInt32)bytesPerSample;
audioFormat.mBytesPerFrame      = (UInt32)bytesPerSample;

CheckError(AudioUnitSetProperty(audioState.rio,
                                kAudioUnitProperty_StreamFormat,
                                kAudioUnitScope_Output,
                                INPUT_BUS,
                                &audioFormat,
                                sizeof(audioFormat)), "Could not set RIO input stream format");

CheckError(AudioUnitSetProperty(audioState.rio,
                                kAudioUnitProperty_StreamFormat,
                                kAudioUnitScope_Input,
                                OUTPUT_BUS,
                                &audioFormat,
                                sizeof(audioFormat)), "Could not set RIO output stream format");


AURenderCallbackStruct callbackStruct;

// Set input callback
callbackStruct.inputProc = &recordingCallback;
callbackStruct.inputProcRefCon = &audioState;
CheckError(AudioUnitSetProperty(audioState.rio,
                                kAudioOutputUnitProperty_SetInputCallback,
                                kAudioUnitScope_Global,
                                INPUT_BUS,
                                &callbackStruct,
                                sizeof(callbackStruct)), "Could not set callback for recording");

// Set output callback
callbackStruct.inputProc = &playbackCallback;
callbackStruct.inputProcRefCon = &audioState;
CheckError(AudioUnitSetProperty(audioState.rio,
                                kAudioUnitProperty_SetRenderCallback,
                                kAudioUnitScope_Global,
                                OUTPUT_BUS,
                                &callbackStruct,
                                sizeof(callbackStruct)), "Could not set callback for playback");