Same here with Logitech BT dongle and MX5500.
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Logitech MX5500 keyboard/mouse does not work with 8.10 install cd (amd64)
https://bugs.launchpad.net/bugs/291269
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ubuntu-bugs mailing
If you have no other BT devices, the quickest solution to a working
keyboard and mouse is to remove bluez and bluetooth 4.12-0ubuntu5
altogether and reseat your USB dongle. The keyboard and mouse will be
detected as USB HIDs.
From a terminal just -
sudo apt-get remove bluez bluetooth
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