I use preview a lot so I saw this as well - I think the problem is that Preview has changed a bit in that you now have previous and next page -in full screen this is back and foward. I simply cusomised the left and right by making two new custom actors for left and right and mapping them with the left and right keyboard arrow keystrokes.

Felix, I'm on Leo 10.5.1 / Preview is 4.0 (469) and the keymap is the latest one that came with Remote Buddy.

A big thankyou for the last update - fixed a real lot of glitches with Leo (using an apple remote to wake my Quad is wicked)