It could be your MS Mobile BT stack. Validate its functions with other BT devices.

I have an HTC phone with a "cooked" MS Mobile 6.X OS. I keep my BT on all of the time. I typically use one of three BT earphones, one of two stereo BT headsets and BT in two BMW's and the BT stack works fine with all.

I typically don't have any pairing problems with the X3 BT. Wondering why you are turning on and off your bluetooth?

My HTC BT settings are as follows:
I have BT turned on but not the checkbox for making the device visible to other devices. I am using radio firmware OS version 1.71.09.01

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E83 - Aero PKG Mods installed: Homelink mirror. CIS-IBUS video module, AUX, Rr Dr Release, stock wheels, Remote start, CarPC (Atom) & mud flaps - NAV - MKIV - NA Map DVD - 2011
E46 - 18.5 wheels/tires (summer), 17 stock (winter), Homelink, NAV software upgrade, BMW video module, Radio to V53, AUX, USB IBUS interface,BMW alarm install, CarPC(Epia), remote starter, tank battery & angel eyes. NAV - MKIII - NA Map CD - High Version 2008.1