Comment 6 for bug 138834

To remove Bluetooth devices manually:
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I had to remove devices manually. The gnome applet asks hcid daemon for known devices.

hcid database is on /var/lib/bluetooth/[YOUR-DONGLE-MAC-ADDRESS] . There are several text files for several purposes: remove the line matching the mac address of the old bluetooth device on each file and you're done.
I had to remove lines from the files sdp, manufacturers, features, classes, lastused, lastseen, names.
If you don't know what mac addresses to remove, the names file can help you because associates a mac address with a device name.
Remember: these files must be edited as root.

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Source: http://ubuntuforums.org/showpost.php?p=6454679&postcount=3