Yea... The 650 has something weird in it's Bluetooth. I'm not sure if it's a driver issue or it's chipset. But for some reason the 650's Bluetooth isn't as compatible with other Bluetooth devices as with other phones.
I have a motorcycle Bluetooth intercom (Sena SMH10) that just doesn't work 100% with my 650. I can pair the SMH10 with just about
any other phone on the planet and it works properly with all it's features, but not with the 650.
I've paired the intercom with other Windows phones (Nokia, Microsoft, and others) at the Microsoft Store and it's fine, again just the 650 has issues. Trying to get MS to look into it, has been rather futile.
And, yes... I have the current firmware installed