That's one weird security feature. I just tried without touching the side rails and sure enough, nothing, but as soon as I touched the rail with just one finger the fingerprint scanner worked.
Ok, I just deleted my fingerprints and tried to add them without touching the side rails and it wouldn't let me do it until I touched the side rail. I wonder why they set it up like that.
I tried it in portrait mode holding the top and bottom. If you had it in landscape the top and bottom would be the sides or did you mean the left and right sides as your holding in in landscape position?
Does that fingerprint only work when you hold it in that position, or will that fingerprint work if you are holding it normally with a case on as well?