I've got a Belkin F8T012uk1 USB Bluetooth adapter.

From usbdevs -v:
  port 1 addr 2: full speed, power 100 mA, config 1, BELKIN BLUETOOTH USB 
ADAPTE CL. 1(0x0121), Broadcom Corp(0x050d), rev 1.00

aue tries to attach:
aue0 at uhub0 port 1
aue0: Broadcom Corp BELKIN BLUETOOTH USB ADAPTER CL. 1, rev 2.00/1.00, addr 2

Which is one of these:
http://catalog.belkin.com/IWCatProductPage.process?Merchant_Id=1&Product_Id=104991

If I stop aue attaching, I get the following and Bluetooth works well:
ubt0 at uhub0 port 1 configuration 1 interface 0
ubt0: Broadcom Corp BELKIN BLUETOOTH USB ADAPTER CL. 1, rev 2.00/1.00, addr 2

So, it looks like there's a duplicate product ID and because the more 
specific product/vendor match beats the class-based match in ubt, ubt is 
not seeing it.

Shall I look at adding a quirk for this device in if_aue.c that will 
check the product class before attaching?

-- 
Stephen