iOS 18: CallKit screen briefly enters foreground when accepting the call via Bluetooth headphones

Hello. We are using Twilio Video SDK and CallKit to report an incoming invite to join a video room. We noticed that on iOS 18 beta when accepting the incoming call invite using Bluetooth headphones while the application is in the foreground, the CallKit screen for a moment enters the foreground before going into background. On iOS 17 when the call invite is accepted, the application remains in foreground and the CallKit screen is instantly sent to background.

What were the headphones involved? Where these "headphones" (meaning, A2DP headphones which ONLY play audio)? Or was this a "hands free headset" (meaning, an HFP capable device which can record audio as well as play)? The "split" between A2DP and HFP means that very similar seeming accessories end up going through totally different code paths, which creates plenty of opportunity for things to go wrong.

Also, do does this happen in SpeakerBox?

This is not reproducible when using Apple EarPods on iOS 18 with a Lightning connector. This seems like a minor change. But it would be nice to know if this is an intentional change or a possible issue.

Assuming this happens in SpeakerBox, then this sounds like a bug and, if you haven't already, I'd recommend filing your own report about it.

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Kevin Elliott
DTS Engineer, CoreOS/Hardware