system sounds aren't affected by device volume for some users

I have a universal app that uses a combination of SystemSounds and AVAudioPlayer sounds. Everything works fine on all of my devices. However, I've had a couple reports from users that the system sounds play at what seems to be the device's full volume level regardless of the actual volume level set for the device. In other words, pressing the hardware buttons on the side of the device changes the AVAudioPlayer sounds, but the system sounds remain at full volume at all times.

Here's the info I've been able to gather so far:

• One of the users' devices is an iPod touch 4th generation and the other is an iPad 2. I don't have access to that iPod model, but I did test with an iPad 2 with no problems. I haven't had reports from iPhone users, so I don't think it's an issue of confusion between the music volume and ringer volume, because these devices don't have a ringer.

• I've asked the users to fully quit the app using the task manager, and also to restart their devices, but the problem remained after both of these steps.

• I'm initializing an audio session with the MediaPlayback category and with MixWithOthers enabled, to control the AVAudioPlayer sounds. I have another that only uses system sounds and doesn't initialize an audio session, so I asked one of the users to try that app. He reported that the sounds are stuck at full volume with that app, too.

Can anyone suggest why this might be happening? Or is there any further troubleshooting I should ask these users to do, since I can't repeat the problem myself?

开发者_开发技巧Update: Perhaps I could ask users to compare the volume behavior in my apps to the volume in a default Apple app or a simple, free app they could install -- does anyone know of an app that uses system sounds? Then I could at least tell if the problem is specific to my app or general to the device.

"Let me amend something here as I just discovered a new setting that FIXES this problem. Go to settings > sounds > "change with buttons". Turn it on. Problem solved!" @ https://discussions.apple.com/thread/2790023?threadID=2790023 ??