This is probably a result of the headphones being connected in headset mode, meaning the microphone is enabled. On Windows when you pair headphones which have a built in microphone you'll usually see two devices connected in the audio switcher, one for the headphones in headset mode and another for the headphones in listening mode only. Headset mode switches to the highly compressed SBC codec so it can transmit both input and output, but listening mode will usually switch to a less compressed codec like AptX, depending on your Windows device. Try pairing again and clicking on the volume button in the systray and see if you have another option for the headphones to switch to.