If by re-tune them, you mean that you need to pair them with the TV again, then the reason is that you can pair you headphones with many separate Bluetooth devices (phone, computer, etc.), but you can only pair them to one other device at a time. Your phones are probably looking for devices to pair with.
If you go to your phone's settings page, connectivity and look for Bluetooth, and show devices you phone will probably see the headphones if they are switched on.