I've successfully paired by bluetooth keyboard with my Microsoft Lumia 640 and it works great - mostly.
The letters, digits and Enter key all work as expected, but the arrow keys are behaving very oddly.
The ▲ key goes up and then types &.
The ▼ key goes down and then types a (.
The ◀ key inserts a % and then goes left.
The ▶ key inserts a ' and then goes right.
(I wish I were joking.)
The same keyboard works fine, including arrow keys, with my Acer Iconia tablet running Windows 8.1.
Please, what's going on? Many thanks.