Am I understanding you correctly that it's possible to somehow disable this feature or something? If so, can you share?
The "Manage sound devices" panel should show a list of "Output devices" and a list of "Input devices." Click on one to disclose a Test button and a Disable button. You should see your headphones show up twice in the "Output devices" menu. Testing one of them will result in a clean sound, the other will result in shit sound (due to SelfVoice). Press "Disable" on the one with shit sound.
Then do it again next time Windows Update runs and clears your user settings, and again, and again, because apparently clearing settings to default is something that Windows Update does now (I've seen it in other places too).
* They're possibly moving to having only the Spring updates do this.
> In several conversations with customers, there was some confusion about noise cancellation function during a phone call or other Bluetooth HFP connection.
Yeah, because having multiple bluetooth profiles, one of which has good cancellation and one of which doesn't due to SelfVoice is disastrous UX.
Anything that perturbs the bluetooth settings on sound-producing devices and switches the default connected endpoint is going to trigger a severe degradation of the headphones' noise cancellation and noise floor. There is no light, or button, or obvious cue to indicate that the device is in a special state. Fixing the problem requires understanding this weird, hidden behavior (strike one) and dealing with bluetooth settings (strike two) on a device that isn't the headphone (strike three).
I am very happy to hear that they are doing something about it, because Windows has recently started clearing my repeated efforts to disable the SelfVoice endpoint. Even though I understand the problem completely (which is always the biggest hurdle) dealing with it has recently become a severe enough hassle that I've been considering ditching the Bose on account of it.