Bluetooth headphones do not connect with full audio capabilities. Only with ' headset' mono sound.
solution:
1) Go to: Control Panel\All Control Panel Items\Devices and Printers
2) Right click the icon of the bluetooth headphones, click 'Properties'
3) Go to the tab Services, uncheck all, leave checked ONLY 'Audio Sink' and 'Remote Control'
https://superuser.com/questions/724018/bad-sound-through-bluetooth-headphones